Advanced GoogleTest Topics (2024)

Introduction

Now that you have read the GoogleTest Primer and learned how towrite tests using GoogleTest, it’s time to learn some new tricks. This documentwill show you more assertions as well as how to construct complex failuremessages, propagate fatal failures, reuse and speed up your test fixtures, anduse various flags with your tests.

More Assertions

This section covers some less frequently used, but still significant,assertions.

Explicit Success and Failure

See Explicit Success and Failure inthe Assertions Reference.

Exception Assertions

See Exception Assertions in the AssertionsReference.

Predicate Assertions for Better Error Messages

Even though GoogleTest has a rich set of assertions, they can never be complete,as it’s impossible (nor a good idea) to anticipate all scenarios a user mightrun into. Therefore, sometimes a user has to use EXPECT_TRUE() to check acomplex expression, for lack of a better macro. This has the problem of notshowing you the values of the parts of the expression, making it hard tounderstand what went wrong. As a workaround, some users choose to construct thefailure message by themselves, streaming it into EXPECT_TRUE(). However, thisis awkward especially when the expression has side-effects or is expensive toevaluate.

GoogleTest gives you three different options to solve this problem:

Using an Existing Boolean Function

If you already have a function or functor that returns bool (or a type thatcan be implicitly converted to bool), you can use it in a predicateassertion to get the function arguments printed for free. SeeEXPECT_PRED* in the AssertionsReference for details.

Using a Function That Returns an AssertionResult

While EXPECT_PRED*() and friends are handy for a quick job, the syntax is notsatisfactory: you have to use different macros for different arities, and itfeels more like Lisp than C++. The ::testing::AssertionResult class solvesthis problem.

An AssertionResult object represents the result of an assertion (whether it’sa success or a failure, and an associated message). You can create anAssertionResult using one of these factory functions:

namespace testing {// Returns an AssertionResult object to indicate that an assertion has// succeeded.AssertionResult AssertionSuccess();// Returns an AssertionResult object to indicate that an assertion has// failed.AssertionResult AssertionFailure();}

You can then use the << operator to stream messages to the AssertionResultobject.

To provide more readable messages in Boolean assertions (e.g. EXPECT_TRUE()),write a predicate function that returns AssertionResult instead of bool. Forexample, if you define IsEven() as:

testing::AssertionResult IsEven(int n) { if ((n % 2) == 0) return testing::AssertionSuccess(); else return testing::AssertionFailure() << n << " is odd";}

instead of:

bool IsEven(int n) { return (n % 2) == 0;}

the failed assertion EXPECT_TRUE(IsEven(Fib(4))) will print:

Value of: IsEven(Fib(4)) Actual: false (3 is odd)Expected: true

instead of a more opaque

Value of: IsEven(Fib(4)) Actual: falseExpected: true

If you want informative messages in EXPECT_FALSE and ASSERT_FALSE as well(one third of Boolean assertions in the Google code base are negative ones), andare fine with making the predicate slower in the success case, you can supply asuccess message:

testing::AssertionResult IsEven(int n) { if ((n % 2) == 0) return testing::AssertionSuccess() << n << " is even"; else return testing::AssertionFailure() << n << " is odd";}

Then the statement EXPECT_FALSE(IsEven(Fib(6))) will print

 Value of: IsEven(Fib(6)) Actual: true (8 is even) Expected: false

Using a Predicate-Formatter

If you find the default message generated byEXPECT_PRED* andEXPECT_TRUE unsatisfactory, or somearguments to your predicate do not support streaming to ostream, you caninstead use predicate-formatter assertions to fully customize how themessage is formatted. SeeEXPECT_PRED_FORMAT* in theAssertions Reference for details.

Floating-Point Comparison

See Floating-Point Comparison in theAssertions Reference.

Floating-Point Predicate-Format Functions

Some floating-point operations are useful, but not that often used. In order toavoid an explosion of new macros, we provide them as predicate-format functionsthat can be used in the predicate assertion macroEXPECT_PRED_FORMAT2, forexample:

using ::testing::FloatLE;using ::testing::DoubleLE;...EXPECT_PRED_FORMAT2(FloatLE, val1, val2);EXPECT_PRED_FORMAT2(DoubleLE, val1, val2);

The above code verifies that val1 is less than, or approximately equal to,val2.

Asserting Using gMock Matchers

See EXPECT_THAT in the AssertionsReference.

More String Assertions

(Please read the previous section first ifyou haven’t.)

You can use the gMock string matcherswith EXPECT_THAT to do more stringcomparison tricks (sub-string, prefix, suffix, regular expression, and etc). Forexample,

using ::testing::HasSubstr;using ::testing::MatchesRegex;... ASSERT_THAT(foo_string, HasSubstr("needle")); EXPECT_THAT(bar_string, MatchesRegex("\\w*\\d+"));

Windows HRESULT assertions

See Windows HRESULT Assertions in theAssertions Reference.

Type Assertions

You can call the function

::testing::StaticAssertTypeEq<T1, T2>();

to assert that types T1 and T2 are the same. The function does nothing ifthe assertion is satisfied. If the types are different, the function call willfail to compile, the compiler error message will say that T1 and T2 are not thesame type and most likely (depending on the compiler) show you the actualvalues of T1 and T2. This is mainly useful inside template code.

Caveat: When used inside a member function of a class template or a functiontemplate, StaticAssertTypeEq<T1, T2>() is effective only if the function isinstantiated. For example, given:

template <typename T> class Foo { public: void Bar() { testing::StaticAssertTypeEq<int, T>(); }};

the code:

void Test1() { Foo<bool> foo; }

will not generate a compiler error, as Foo<bool>::Bar() is never actuallyinstantiated. Instead, you need:

void Test2() { Foo<bool> foo; foo.Bar(); }

to cause a compiler error.

Assertion Placement

You can use assertions in any C++ function. In particular, it doesn’t have to bea method of the test fixture class. The one constraint is that assertions thatgenerate a fatal failure (FAIL* and ASSERT_*) can only be used invoid-returning functions. This is a consequence of Google’s not usingexceptions. By placing it in a non-void function you’ll get a confusing compileerror like "error: void value not ignored as it ought to be" or "cannotinitialize return object of type 'bool' with an rvalue of type 'void'" or"error: no viable conversion from 'void' to 'string'".

If you need to use fatal assertions in a function that returns non-void, oneoption is to make the function return the value in an out parameter instead. Forexample, you can rewrite T2 Foo(T1 x) to void Foo(T1 x, T2* result). Youneed to make sure that *result contains some sensible value even when thefunction returns prematurely. As the function now returns void, you can useany assertion inside of it.

If changing the function’s type is not an option, you should just use assertionsthat generate non-fatal failures, such as ADD_FAILURE* and EXPECT_*.

NOTE: Constructors and destructors are not considered void-returning functions,according to the C++ language specification, and so you may not use fatalassertions in them; you’ll get a compilation error if you try. Instead, eithercall abort and crash the entire test executable, or put the fatal assertion ina SetUp/TearDown function; seeconstructor/destructor vs. SetUp/TearDown

WARNING: A fatal assertion in a helper function (private void-returning method)called from a constructor or destructor does not terminate the current test, asyour intuition might suggest: it merely returns from the constructor ordestructor early, possibly leaving your object in a partially-constructed orpartially-destructed state! You almost certainly want to abort or useSetUp/TearDown instead.

Skipping test execution

Related to the assertions SUCCEED() and FAIL(), you can prevent further testexecution at runtime with the GTEST_SKIP() macro. This is useful when you needto check for preconditions of the system under test during runtime and skiptests in a meaningful way.

GTEST_SKIP() can be used in individual test cases or in the SetUp() methodsof classes derived from either ::testing::Environment or ::testing::Test.For example:

TEST(SkipTest, DoesSkip) { GTEST_SKIP() << "Skipping single test"; EXPECT_EQ(0, 1); // Won't fail; it won't be executed}class SkipFixture : public ::testing::Test { protected: void SetUp() override { GTEST_SKIP() << "Skipping all tests for this fixture"; }};// Tests for SkipFixture won't be executed.TEST_F(SkipFixture, SkipsOneTest) { EXPECT_EQ(5, 7); // Won't fail}

As with assertion macros, you can stream a custom message into GTEST_SKIP().

Teaching GoogleTest How to Print Your Values

When a test assertion such as EXPECT_EQ fails, GoogleTest prints the argumentvalues to help you debug. It does this using a user-extensible value printer.

This printer knows how to print built-in C++ types, native arrays, STLcontainers, and any type that supports the << operator. For other types, itprints the raw bytes in the value and hopes that you the user can figure it out.

As mentioned earlier, the printer is extensible. That means you can teach itto do a better job at printing your particular type than to dump the bytes. Todo that, define an AbslStringify() overload as a friend function templatefor your type:

namespace foo {class Point { // We want GoogleTest to be able to print instances of this. ... // Provide a friend overload. template <typename Sink> friend void AbslStringify(Sink& sink, const Point& point) { absl::Format(&sink, "(%d, %d)", point.x, point.y); } int x; int y;};// If you can't declare the function in the class it's important that the// AbslStringify overload is defined in the SAME namespace that defines Point.// C++'s look-up rules rely on that.enum class EnumWithStringify { kMany = 0, kChoices = 1 };template <typename Sink>void AbslStringify(Sink& sink, EnumWithStringify e) { absl::Format(&sink, "%s", e == EnumWithStringify::kMany ? "Many" : "Choices");}} // namespace foo

Note: AbslStringify() utilizes a generic “sink” buffer to construct itsstring. For more information about supported operations on AbslStringify()’ssink, see go/abslstringify.

AbslStringify() can also use absl::StrFormat’s catch-all %v type specifierwithin its own format strings to perform type deduction. Point above could beformatted as "(%v, %v)" for example, and deduce the int values as %d.

Sometimes, AbslStringify() might not be an option: your team may wish to printtypes with extra debugging information for testing purposes only. If so, you caninstead define a PrintTo() function like this:

#include <ostream>namespace foo {class Point { ... friend void PrintTo(const Point& point, std::ostream* os) { *os << "(" << point.x << "," << point.y << ")"; } int x; int y;};// If you can't declare the function in the class it's important that PrintTo()// is defined in the SAME namespace that defines Point. C++'s look-up rules// rely on that.void PrintTo(const Point& point, std::ostream* os) { *os << "(" << point.x << "," << point.y << ")";}} // namespace foo

If you have defined both AbslStringify() and PrintTo(), the latter will beused by GoogleTest. This allows you to customize how the value appears inGoogleTest’s output without affecting code that relies on the behavior ofAbslStringify().

If you have an existing << operator and would like to define anAbslStringify(), the latter will be used for GoogleTest printing.

If you want to print a value x using GoogleTest’s value printer yourself, justcall ::testing::PrintToString(x), which returns an std::string:

vector<pair<Point, int> > point_ints = GetPointIntVector();EXPECT_TRUE(IsCorrectPointIntVector(point_ints)) << "point_ints = " << testing::PrintToString(point_ints);

For more details regarding AbslStringify() and its integration with otherlibraries, see go/abslstringify.

Death Tests

In many applications, there are assertions that can cause application failure ifa condition is not met. These consistency checks, which ensure that the programis in a known good state, are there to fail at the earliest possible time aftersome program state is corrupted. If the assertion checks the wrong condition,then the program may proceed in an erroneous state, which could lead to memorycorruption, security holes, or worse. Hence it is vitally important to test thatsuch assertion statements work as expected.

Since these precondition checks cause the processes to die, we call such testsdeath tests. More generally, any test that checks that a program terminates(except by throwing an exception) in an expected fashion is also a death test.

Note that if a piece of code throws an exception, we don’t consider it “death”for the purpose of death tests, as the caller of the code could catch theexception and avoid the crash. If you want to verify exceptions thrown by yourcode, see Exception Assertions.

If you want to test EXPECT_*()/ASSERT_*() failures in your test code, see“Catching” Failures.

How to Write a Death Test

GoogleTest provides assertion macros to support death tests. SeeDeath Assertions in the Assertions Referencefor details.

To write a death test, simply use one of the macros inside your test function.For example,

TEST(MyDeathTest, Foo) { // This death test uses a compound statement. ASSERT_DEATH({ int n = 5; Foo(&n); }, "Error on line .* of Foo()");}TEST(MyDeathTest, NormalExit) { EXPECT_EXIT(NormalExit(), testing::ExitedWithCode(0), "Success");}TEST(MyDeathTest, KillProcess) { EXPECT_EXIT(KillProcess(), testing::KilledBySignal(SIGKILL), "Sending myself unblockable signal");}

verifies that:

• calling Foo(5) causes the process to die with the given error message,
• calling NormalExit() causes the process to print "Success" to stderr andexit with exit code 0, and
• calling KillProcess() kills the process with signal SIGKILL.

The test function body may contain other assertions and statements as well, ifnecessary.

Note that a death test only cares about three things:

1. does statement abort or exit the process?
2. (in the case of ASSERT_EXIT and EXPECT_EXIT) does the exit statussatisfy predicate? Or (in the case of ASSERT_DEATH and EXPECT_DEATH)is the exit status non-zero? And
3. does the stderr output match matcher?

In particular, if statement generates an ASSERT_* or EXPECT_* failure, itwill not cause the death test to fail, as GoogleTest assertions don’t abortthe process.

Death Test Naming

IMPORTANT: We strongly recommend you to follow the convention of naming yourtest suite (not test) *DeathTest when it contains a death test, asdemonstrated in the above example. TheDeath Tests And Threads section below explains why.

If a test fixture class is shared by normal tests and death tests, you can useusing or typedef to introduce an alias for the fixture class and avoidduplicating its code:

class FooTest : public testing::Test { ... };using FooDeathTest = FooTest;TEST_F(FooTest, DoesThis) { // normal test}TEST_F(FooDeathTest, DoesThat) { // death test}

Regular Expression Syntax

When built with Bazel and using Abseil, GoogleTest uses theRE2 syntax. Otherwise, for POSIXsystems (Linux, Cygwin, Mac), GoogleTest uses thePOSIX extended regular expressionsyntax. To learn about POSIX syntax, you may want to read thisWikipedia entry.

On Windows, GoogleTest uses its own simple regular expression implementation. Itlacks many features. For example, we don’t support union ("x|y"), grouping("(xy)"), brackets ("[xy]"), and repetition count ("x{5,7}"), amongothers. Below is what we do support (A denotes a literal character, period(.), or a single \\ escape sequence; x and y denote regularexpressions.):

To help you determine which capability is available on your system, GoogleTestdefines macros to govern which regular expression it is using. The macros are:GTEST_USES_SIMPLE_RE=1 or GTEST_USES_POSIX_RE=1. If you want your deathtests to work in all cases, you can either #if on these macros or use the morelimited syntax only.

How It Works

See Death Assertions in the AssertionsReference.

Death Tests And Threads

The reason for the two death test styles has to do with thread safety. Due towell-known problems with forking in the presence of threads, death tests shouldbe run in a single-threaded context. Sometimes, however, it isn’t feasible toarrange that kind of environment. For example, statically-initialized modulesmay start threads before main is ever reached. Once threads have been created,it may be difficult or impossible to clean them up.

GoogleTest has three features intended to raise awareness of threading issues.

1. A warning is emitted if multiple threads are running when a death test isencountered.
2. Test suites with a name ending in “DeathTest” are run before all othertests.
3. It uses clone() instead of fork() to spawn the child process on Linux(clone() is not available on Cygwin and Mac), as fork() is more likelyto cause the child to hang when the parent process has multiple threads.

It’s perfectly fine to create threads inside a death test statement; they areexecuted in a separate process and cannot affect the parent.

Death Test Styles

The “threadsafe” death test style was introduced in order to help mitigate therisks of testing in a possibly multithreaded environment. It trades increasedtest execution time (potentially dramatically so) for improved thread safety.

The automated testing framework does not set the style flag. You can choose aparticular style of death tests by setting the flag programmatically:

GTEST_FLAG_SET(death_test_style, "threadsafe");

You can do this in main() to set the style for all death tests in the binary,or in individual tests. Recall that flags are saved before running each test andrestored afterwards, so you need not do that yourself. For example:

int main(int argc, char** argv) { testing::InitGoogleTest(&argc, argv); GTEST_FLAG_SET(death_test_style, "fast"); return RUN_ALL_TESTS();}TEST(MyDeathTest, TestOne) { GTEST_FLAG_SET(death_test_style, "threadsafe"); // This test is run in the "threadsafe" style: ASSERT_DEATH(ThisShouldDie(), "");}TEST(MyDeathTest, TestTwo) { // This test is run in the "fast" style: ASSERT_DEATH(ThisShouldDie(), "");}

Caveats

The statement argument of ASSERT_EXIT() can be any valid C++ statement. Ifit leaves the current function via a return statement or by throwing anexception, the death test is considered to have failed. Some GoogleTest macrosmay return from the current function (e.g. ASSERT_TRUE()), so be sure to avoidthem in statement.

Since statement runs in the child process, any in-memory side effect (e.g.modifying a variable, releasing memory, etc) it causes will not be observablein the parent process. In particular, if you release memory in a death test,your program will fail the heap check as the parent process will never see thememory reclaimed. To solve this problem, you can

1. try not to free memory in a death test;
2. free the memory again in the parent process; or
3. do not use the heap checker in your program.

Due to an implementation detail, you cannot place multiple death test assertionson the same line; otherwise, compilation will fail with an unobvious errormessage.

Despite the improved thread safety afforded by the “threadsafe” style of deathtest, thread problems such as deadlock are still possible in the presence ofhandlers registered with pthread_atfork(3).

Using Assertions in Sub-routines

Note: If you want to put a series of test assertions in a subroutine to checkfor a complex condition, consider usinga custom GMock matcher instead. This lets youprovide a more readable error message in case of failure and avoid all of theissues described below.

Adding Traces to Assertions

If a test sub-routine is called from several places, when an assertion inside itfails, it can be hard to tell which invocation of the sub-routine the failure isfrom. You can alleviate this problem using extra logging or custom failuremessages, but that usually clutters up your tests. A better solution is to usethe SCOPED_TRACE macro or the ScopedTrace utility:

SCOPED_TRACE(message);

ScopedTrace trace("file_path", line_number, message);

where message can be anything streamable to std::ostream. SCOPED_TRACEmacro will cause the current file name, line number, and the given message to beadded in every failure message. ScopedTrace accepts explicit file name andline number in arguments, which is useful for writing test helpers. The effectwill be undone when the control leaves the current lexical scope.

For example,

10: void Sub1(int n) {11: EXPECT_EQ(Bar(n), 1);12: EXPECT_EQ(Bar(n + 1), 2);13: }14:15: TEST(FooTest, Bar) {16: {17: SCOPED_TRACE("A"); // This trace point will be included in18: // every failure in this scope.19: Sub1(1);20: }21: // Now it won't.22: Sub1(9);23: }

could result in messages like these:

path/to/foo_test.cc:11: FailureValue of: Bar(n)Expected: 1 Actual: 2Google Test trace:path/to/foo_test.cc:17: Apath/to/foo_test.cc:12: FailureValue of: Bar(n + 1)Expected: 2 Actual: 3

Without the trace, it would’ve been difficult to know which invocation ofSub1() the two failures come from respectively. (You could add an extramessage to each assertion in Sub1() to indicate the value of n, but that’stedious.)

Some tips on using SCOPED_TRACE:

1. With a suitable message, it’s often enough to use SCOPED_TRACE at thebeginning of a sub-routine, instead of at each call site.
2. When calling sub-routines inside a loop, make the loop iterator part of themessage in SCOPED_TRACE such that you can know which iteration the failureis from.
3. Sometimes the line number of the trace point is enough for identifying theparticular invocation of a sub-routine. In this case, you don’t have tochoose a unique message for SCOPED_TRACE. You can simply use "".
4. You can use SCOPED_TRACE in an inner scope when there is one in the outerscope. In this case, all active trace points will be included in the failuremessages, in reverse order they are encountered.
5. The trace dump is clickable in Emacs - hit return on a line number andyou’ll be taken to that line in the source file!

Propagating Fatal Failures

A common pitfall when using ASSERT_* and FAIL* is not understanding thatwhen they fail they only abort the current function, not the entire test. Forexample, the following test will segfault:

void Subroutine() { // Generates a fatal failure and aborts the current function. ASSERT_EQ(1, 2); // The following won't be executed. ...}TEST(FooTest, Bar) { Subroutine(); // The intended behavior is for the fatal failure // in Subroutine() to abort the entire test. // The actual behavior: the function goes on after Subroutine() returns. int* p = nullptr; *p = 3; // Segfault!}

To alleviate this, GoogleTest provides three different solutions. You could useeither exceptions, the (ASSERT|EXPECT)_NO_FATAL_FAILURE assertions or theHasFatalFailure() function. They are described in the following twosubsections.

Asserting on Subroutines with an exception

The following code can turn ASSERT-failure into an exception:

class ThrowListener : public testing::EmptyTestEventListener { void OnTestPartResult(const testing::TestPartResult& result) override { if (result.type() == testing::TestPartResult::kFatalFailure) { throw testing::AssertionException(result); } }};int main(int argc, char** argv) { ... testing::UnitTest::GetInstance()->listeners().Append(new ThrowListener); return RUN_ALL_TESTS();}

This listener should be added after other listeners if you have any, otherwisethey won’t see failed OnTestPartResult.

Asserting on Subroutines

As shown above, if your test calls a subroutine that has an ASSERT_* failurein it, the test will continue after the subroutine returns. This may not be whatyou want.

Often people want fatal failures to propagate like exceptions. For thatGoogleTest offers the following macros:

Only failures in the thread that executes the assertion are checked to determinethe result of this type of assertions. If statement creates new threads,failures in these threads are ignored.

Examples:

ASSERT_NO_FATAL_FAILURE(Foo());int i;EXPECT_NO_FATAL_FAILURE({ i = Bar();});

Assertions from multiple threads are currently not supported on Windows.

Checking for Failures in the Current Test

HasFatalFailure() in the ::testing::Test class returns true if anassertion in the current test has suffered a fatal failure. This allowsfunctions to catch fatal failures in a sub-routine and return early.

class Test { public: ... static bool HasFatalFailure();};

The typical usage, which basically simulates the behavior of a thrown exception,is:

TEST(FooTest, Bar) { Subroutine(); // Aborts if Subroutine() had a fatal failure. if (HasFatalFailure()) return; // The following won't be executed. ...}

If HasFatalFailure() is used outside of TEST() , TEST_F() , or a testfixture, you must add the ::testing::Test:: prefix, as in:

if (testing::Test::HasFatalFailure()) return;

Similarly, HasNonfatalFailure() returns true if the current test has atleast one non-fatal failure, and HasFailure() returns true if the currenttest has at least one failure of either kind.

Logging Additional Information

In your test code, you can call RecordProperty("key", value) to log additionalinformation, where value can be either a string or an int. The last valuerecorded for a key will be emitted to theXML output if you specify one. For example, thetest

TEST_F(WidgetUsageTest, MinAndMaxWidgets) { RecordProperty("MaximumWidgets", ComputeMaxUsage()); RecordProperty("MinimumWidgets", ComputeMinUsage());}

will output XML like this:

 ... <testcase name="MinAndMaxWidgets" file="test.cpp" line="1" status="run" time="0.006" classname="WidgetUsageTest" MaximumWidgets="12" MinimumWidgets="9" /> ...

NOTE:

• RecordProperty() is a static member of the Test class. Therefore itneeds to be prefixed with ::testing::Test:: if used outside of theTEST body and the test fixture class.
• key must be a valid XML attribute name, and cannot conflict with theones already used by GoogleTest (name, status, time, classname,type_param, and value_param).
• Calling RecordProperty() outside of the lifespan of a test is allowed.If it’s called outside of a test but between a test suite’sSetUpTestSuite() and TearDownTestSuite() methods, it will beattributed to the XML element for the test suite. If it’s called outsideof all test suites (e.g. in a test environment), it will be attributed tothe top-level XML element.

Sharing Resources Between Tests in the Same Test Suite

GoogleTest creates a new test fixture object for each test in order to maketests independent and easier to debug. However, sometimes tests use resourcesthat are expensive to set up, making the one-copy-per-test model prohibitivelyexpensive.

If the tests don’t change the resource, there’s no harm in their sharing asingle resource copy. So, in addition to per-test set-up/tear-down, GoogleTestalso supports per-test-suite set-up/tear-down. To use it:

1. In your test fixture class (say FooTest ), declare as static some membervariables to hold the shared resources.
2. Outside your test fixture class (typically just below it), define thosemember variables, optionally giving them initial values.
3. In the same test fixture class, define a public member function static voidSetUpTestSuite() (remember not to spell it as SetupTestSuite with asmall u!) to set up the shared resources and a static voidTearDownTestSuite() function to tear them down.

That’s it! GoogleTest automatically calls SetUpTestSuite() before running thefirst test in the FooTest test suite (i.e. before creating the firstFooTest object), and calls TearDownTestSuite() after running the last testin it (i.e. after deleting the last FooTest object). In between, the tests canuse the shared resources.

Remember that the test order is undefined, so your code can’t depend on a testpreceding or following another. Also, the tests must either not modify the stateof any shared resource, or, if they do modify the state, they must restore thestate to its original value before passing control to the next test.

Note that SetUpTestSuite() may be called multiple times for a test fixtureclass that has derived classes, so you should not expect code in the functionbody to be run only once. Also, derived classes still have access to sharedresources defined as static members, so careful consideration is needed whenmanaging shared resources to avoid memory leaks if shared resources are notproperly cleaned up in TearDownTestSuite().

Here’s an example of per-test-suite set-up and tear-down:

class FooTest : public testing::Test { protected: // Per-test-suite set-up. // Called before the first test in this test suite. // Can be omitted if not needed. static void SetUpTestSuite() { shared_resource_ = new ...; // If `shared_resource_` is **not deleted** in `TearDownTestSuite()`, // reallocation should be prevented because `SetUpTestSuite()` may be called // in subclasses of FooTest and lead to memory leak. // // if (shared_resource_ == nullptr) { // shared_resource_ = new ...; // } } // Per-test-suite tear-down. // Called after the last test in this test suite. // Can be omitted if not needed. static void TearDownTestSuite() { delete shared_resource_; shared_resource_ = nullptr; } // You can define per-test set-up logic as usual. void SetUp() override { ... } // You can define per-test tear-down logic as usual. void TearDown() override { ... } // Some expensive resource shared by all tests. static T* shared_resource_;};T* FooTest::shared_resource_ = nullptr;TEST_F(FooTest, Test1) { ... you can refer to shared_resource_ here ...}TEST_F(FooTest, Test2) { ... you can refer to shared_resource_ here ...}

NOTE: Though the above code declares SetUpTestSuite() protected, it maysometimes be necessary to declare it public, such as when using it withTEST_P.

Global Set-Up and Tear-Down

Just as you can do set-up and tear-down at the test level and the test suitelevel, you can also do it at the test program level. Here’s how.

First, you subclass the ::testing::Environment class to define a testenvironment, which knows how to set-up and tear-down:

class Environment : public ::testing::Environment { public: ~Environment() override {} // Override this to define how to set up the environment. void SetUp() override {} // Override this to define how to tear down the environment. void TearDown() override {}};

Then, you register an instance of your environment class with GoogleTest bycalling the ::testing::AddGlobalTestEnvironment() function:

Environment* AddGlobalTestEnvironment(Environment* env);

Now, when RUN_ALL_TESTS() is invoked, it first calls the SetUp() method. Thetests are then executed, provided that none of the environments have reportedfatal failures and GTEST_SKIP() has not been invoked. Finally, TearDown() iscalled.

Note that SetUp() and TearDown() are only invoked if there is at least onetest to be performed. Importantly, TearDown() is executed even if the test isnot run due to a fatal failure or GTEST_SKIP().

Calling SetUp() and TearDown() for each iteration depends on the flaggtest_recreate_environments_when_repeating. SetUp() and TearDown() arecalled for each environment object when the object is recreated for eachiteration. However, if test environments are not recreated for each iteration,SetUp() is called only on the first iteration, and TearDown() is called onlyon the last iteration.

It’s OK to register multiple environment objects. In this suite, their SetUp()will be called in the order they are registered, and their TearDown() will becalled in the reverse order.

Note that GoogleTest takes ownership of the registered environment objects.Therefore do not delete them by yourself.

You should call AddGlobalTestEnvironment() before RUN_ALL_TESTS() is called,probably in main(). If you use gtest_main, you need to call this beforemain() starts for it to take effect. One way to do this is to define a globalvariable like this:

testing::Environment* const foo_env = testing::AddGlobalTestEnvironment(new FooEnvironment);

However, we strongly recommend you to write your own main() and callAddGlobalTestEnvironment() there, as relying on initialization of globalvariables makes the code harder to read and may cause problems when you registermultiple environments from different translation units and the environments havedependencies among them (remember that the compiler doesn’t guarantee the orderin which global variables from different translation units are initialized).

Value-Parameterized Tests

Value-parameterized tests allow you to test your code with differentparameters without writing multiple copies of the same test. This is useful in anumber of situations, for example:

• You have a piece of code whose behavior is affected by one or morecommand-line flags. You want to make sure your code performs correctly forvarious values of those flags.
• You want to test different implementations of an OO interface.
• You want to test your code over various inputs (a.k.a. data-driven testing).This feature is easy to abuse, so please exercise your good sense when doingit!

How to Write Value-Parameterized Tests

To write value-parameterized tests, first you should define a fixture class. Itmust be derived from both testing::Test and testing::WithParamInterface<T>(the latter is a pure interface), where T is the type of your parametervalues. For convenience, you can just derive the fixture class fromtesting::TestWithParam<T>, which itself is derived from both testing::Testand testing::WithParamInterface<T>. T can be any copyable type. If it’s araw pointer, you are responsible for managing the lifespan of the pointedvalues.

NOTE: If your test fixture defines SetUpTestSuite() or TearDownTestSuite()they must be declared public rather than protected in order to useTEST_P.

class FooTest : public testing::TestWithParam<absl::string_view> { // You can implement all the usual fixture class members here. // To access the test parameter, call GetParam() from class // TestWithParam<T>.};// Or, when you want to add parameters to a pre-existing fixture class:class BaseTest : public testing::Test { ...};class BarTest : public BaseTest, public testing::WithParamInterface<absl::string_view> { ...};

Then, use the TEST_P macro to define as many test patterns using this fixtureas you want. The _P suffix is for “parameterized” or “pattern”, whichever youprefer to think.

TEST_P(FooTest, DoesBlah) { // Inside a test, access the test parameter with the GetParam() method // of the TestWithParam<T> class: EXPECT_TRUE(foo.Blah(GetParam())); ...}TEST_P(FooTest, HasBlahBlah) { ...}

Finally, you can use the INSTANTIATE_TEST_SUITE_P macro to instantiate thetest suite with any set of parameters you want. GoogleTest defines a number offunctions for generating test parameters—see details atINSTANTIATE_TEST_SUITE_P inthe Testing Reference.

For example, the following statement will instantiate tests from the FooTesttest suite each with parameter values "meeny", "miny", and "moe" using theValues parameter generator:

INSTANTIATE_TEST_SUITE_P(MeenyMinyMoe, FooTest, testing::Values("meeny", "miny", "moe"));

NOTE: The code above must be placed at global or namespace scope, not atfunction scope.

The first argument to INSTANTIATE_TEST_SUITE_P is a unique name for theinstantiation of the test suite. The next argument is the name of the testpattern, and the last is theparameter generator.

The parameter generator expression is not evaluated until GoogleTest isinitialized (via InitGoogleTest()). Any prior initialization done in themain function will be accessible from the parameter generator, for example,the results of flag parsing.

You can instantiate a test pattern more than once, so to distinguish differentinstances of the pattern, the instantiation name is added as a prefix to theactual test suite name. Remember to pick unique prefixes for differentinstantiations. The tests from the instantiation above will have these names:

• MeenyMinyMoe/FooTest.DoesBlah/0 for "meeny"
• MeenyMinyMoe/FooTest.DoesBlah/1 for "miny"
• MeenyMinyMoe/FooTest.DoesBlah/2 for "moe"
• MeenyMinyMoe/FooTest.HasBlahBlah/0 for "meeny"
• MeenyMinyMoe/FooTest.HasBlahBlah/1 for "miny"
• MeenyMinyMoe/FooTest.HasBlahBlah/2 for "moe"

You can use these names in --gtest_filter.

The following statement will instantiate all tests from FooTest again, eachwith parameter values "cat" and "dog" using theValuesIn parameter generator:

constexpr absl::string_view kPets[] = {"cat", "dog"};INSTANTIATE_TEST_SUITE_P(Pets, FooTest, testing::ValuesIn(kPets));

The tests from the instantiation above will have these names:

• Pets/FooTest.DoesBlah/0 for "cat"
• Pets/FooTest.DoesBlah/1 for "dog"
• Pets/FooTest.HasBlahBlah/0 for "cat"
• Pets/FooTest.HasBlahBlah/1 for "dog"

Please note that INSTANTIATE_TEST_SUITE_P will instantiate all tests in thegiven test suite, whether their definitions come before or after theINSTANTIATE_TEST_SUITE_P statement.

Additionally, by default, every TEST_P without a correspondingINSTANTIATE_TEST_SUITE_P causes a failing test in test suiteGoogleTestVerification. If you have a test suite where that omission is not anerror, for example it is in a library that may be linked in for other reasons orwhere the list of test cases is dynamic and may be empty, then this check can besuppressed by tagging the test suite:

GTEST_ALLOW_UNINSTANTIATED_PARAMETERIZED_TEST(FooTest);

You can see sample7_unittest.cc and sample8_unittest.cc for more examples.

Creating Value-Parameterized Abstract Tests

In the above, we define and instantiate FooTest in the same source file.Sometimes you may want to define value-parameterized tests in a library and letother people instantiate them later. This pattern is known as abstract tests.As an example of its application, when you are designing an interface you canwrite a standard suite of abstract tests (perhaps using a factory function asthe test parameter) that all implementations of the interface are expected topass. When someone implements the interface, they can instantiate your suite toget all the interface-conformance tests for free.

To define abstract tests, you should organize your code like this:

1. Put the definition of the parameterized test fixture class (e.g. FooTest)in a header file, say foo_param_test.h. Think of this as declaring yourabstract tests.
2. Put the TEST_P definitions in foo_param_test.cc, which includesfoo_param_test.h. Think of this as implementing your abstract tests.

Once they are defined, you can instantiate them by including foo_param_test.h,invoking INSTANTIATE_TEST_SUITE_P(), and depending on the library target thatcontains foo_param_test.cc. You can instantiate the same abstract test suitemultiple times, possibly in different source files.

Specifying Names for Value-Parameterized Test Parameters

The optional last argument to INSTANTIATE_TEST_SUITE_P() allows the user tospecify a function or functor that generates custom test name suffixes based onthe test parameters. The function should accept one argument of typetesting::TestParamInfo<class ParamType>, and return std::string.

testing::PrintToStringParamName is a builtin test suffix generator thatreturns the value of testing::PrintToString(GetParam()). It does not work forstd::string or C strings.

NOTE: test names must be non-empty, unique, and may only contain ASCIIalphanumeric characters. In particular, theyshould not contain underscores

class MyTestSuite : public testing::TestWithParam<int> {};TEST_P(MyTestSuite, MyTest){ std::cout << "Example Test Param: " << GetParam() << std::endl;}INSTANTIATE_TEST_SUITE_P(MyGroup, MyTestSuite, testing::Range(0, 10), testing::PrintToStringParamName());

Providing a custom functor allows for more control over test parameter namegeneration, especially for types where the automatic conversion does notgenerate helpful parameter names (e.g. strings as demonstrated above). Thefollowing example illustrates this for multiple parameters, an enumeration typeand a string, and also demonstrates how to combine generators. It uses a lambdafor conciseness:

enum class MyType { MY_FOO = 0, MY_BAR = 1 };class MyTestSuite : public testing::TestWithParam<std::tuple<MyType, std::string>> {};INSTANTIATE_TEST_SUITE_P( MyGroup, MyTestSuite, testing::Combine( testing::Values(MyType::MY_FOO, MyType::MY_BAR), testing::Values("A", "B")), [](const testing::TestParamInfo<MyTestSuite::ParamType>& info) { std::string name = absl::StrCat( std::get<0>(info.param) == MyType::MY_FOO ? "Foo" : "Bar", std::get<1>(info.param)); absl::c_replace_if(name, [](char c) { return !std::isalnum(c); }, '_'); return name; });

Typed Tests

Suppose you have multiple implementations of the same interface and want to makesure that all of them satisfy some common requirements. Or, you may have definedseveral types that are supposed to conform to the same “concept” and you want toverify it. In both cases, you want the same test logic repeated for differenttypes.

While you can write one TEST or TEST_F for each type you want to test (andyou may even factor the test logic into a function template that you invoke fromthe TEST), it’s tedious and doesn’t scale: if you want m tests over ntypes, you’ll end up writing m*n TESTs.

Typed tests allow you to repeat the same test logic over a list of types. Youonly need to write the test logic once, although you must know the type listwhen writing typed tests. Here’s how you do it:

First, define a fixture class template. It should be parameterized by a type.Remember to derive it from ::testing::Test:

template <typename T>class FooTest : public testing::Test { public: ... using List = std::list<T>; static T shared_; T value_;};

Next, associate a list of types with the test suite, which will be repeated foreach type in the list:

using MyTypes = ::testing::Types<char, int, unsigned int>;TYPED_TEST_SUITE(FooTest, MyTypes);

The type alias (using or typedef) is necessary for the TYPED_TEST_SUITEmacro to parse correctly. Otherwise the compiler will think that each comma inthe type list introduces a new macro argument.

Then, use TYPED_TEST() instead of TEST_F() to define a typed test for thistest suite. You can repeat this as many times as you want:

TYPED_TEST(FooTest, DoesBlah) { // Inside a test, refer to the special name TypeParam to get the type // parameter. Since we are inside a derived class template, C++ requires // us to visit the members of FooTest via 'this'. TypeParam n = this->value_; // To visit static members of the fixture, add the 'TestFixture::' // prefix. n += TestFixture::shared_; // To refer to typedefs in the fixture, add the 'typename TestFixture::' // prefix. The 'typename' is required to satisfy the compiler. typename TestFixture::List values; values.push_back(n); ...}TYPED_TEST(FooTest, HasPropertyA) { ... }

You can see sample6_unittest.cc for a complete example.

Type-Parameterized Tests

Type-parameterized tests are like typed tests, except that they don’t requireyou to know the list of types ahead of time. Instead, you can define the testlogic first and instantiate it with different type lists later. You can eveninstantiate it more than once in the same program.

If you are designing an interface or concept, you can define a suite oftype-parameterized tests to verify properties that any valid implementation ofthe interface/concept should have. Then, the author of each implementation canjust instantiate the test suite with their type to verify that it conforms tothe requirements, without having to write similar tests repeatedly. Here’s anexample:

First, define a fixture class template, as we did with typed tests:

template <typename T>class FooTest : public testing::Test { void DoSomethingInteresting(); ...};

Next, declare that you will define a type-parameterized test suite:

TYPED_TEST_SUITE_P(FooTest);

Then, use TYPED_TEST_P() to define a type-parameterized test. You can repeatthis as many times as you want:

TYPED_TEST_P(FooTest, DoesBlah) { // Inside a test, refer to TypeParam to get the type parameter. TypeParam n = 0; // You will need to use `this` explicitly to refer to fixture members. this->DoSomethingInteresting() ...}TYPED_TEST_P(FooTest, HasPropertyA) { ... }

Now the tricky part: you need to register all test patterns using theREGISTER_TYPED_TEST_SUITE_P macro before you can instantiate them. The firstargument of the macro is the test suite name; the rest are the names of thetests in this test suite:

REGISTER_TYPED_TEST_SUITE_P(FooTest, DoesBlah, HasPropertyA);

Finally, you are free to instantiate the pattern with the types you want. If youput the above code in a header file, you can #include it in multiple C++source files and instantiate it multiple times.

using MyTypes = ::testing::Types<char, int, unsigned int>;INSTANTIATE_TYPED_TEST_SUITE_P(My, FooTest, MyTypes);

To distinguish different instances of the pattern, the first argument to theINSTANTIATE_TYPED_TEST_SUITE_P macro is a prefix that will be added to theactual test suite name. Remember to pick unique prefixes for differentinstances.

In the special case where the type list contains only one type, you can writethat type directly without ::testing::Types<...>, like this:

INSTANTIATE_TYPED_TEST_SUITE_P(My, FooTest, int);

You can see sample6_unittest.cc for a complete example.

Testing Private Code

If you change your software’s internal implementation, your tests should notbreak as long as the change is not observable by users. Therefore, per theblack-box testing principle, most of the time you should test your code throughits public interfaces.

If you still find yourself needing to test internal implementation code,consider if there’s a better design. The desire to test internalimplementation is often a sign that the class is doing too much. Considerextracting an implementation class, and testing it. Then use that implementationclass in the original class.

If you absolutely have to test non-public interface code though, you can. Thereare two cases to consider:

• Static functions ( not the same as static member functions!) or unnamednamespaces, and
• Private or protected class members

To test them, we use the following special techniques:

• Both static functions and definitions/declarations in an unnamed namespaceare only visible within the same translation unit. To test them, you can#include the entire .cc file being tested in your *_test.cc file.(#including .cc files is not a good way to reuse code - you should not dothis in production code!)

  However, a better approach is to move the private code into thefoo::internal namespace, where foo is the namespace your projectnormally uses, and put the private declarations in a *-internal.h file.Your production .cc files and your tests are allowed to include thisinternal header, but your clients are not. This way, you can fully test yourinternal implementation without leaking it to your clients.

• Private class members are only accessible from within the class or byfriends. To access a class’ private members, you can declare your testfixture as a friend to the class and define accessors in your fixture. Testsusing the fixture can then access the private members of your productionclass via the accessors in the fixture. Note that even though your fixtureis a friend to your production class, your tests are not automaticallyfriends to it, as they are technically defined in sub-classes of thefixture.

  Another way to test private members is to refactor them into animplementation class, which is then declared in a *-internal.h file. Yourclients aren’t allowed to include this header but your tests can. Such iscalled thePimpl(Private Implementation) idiom.

  Or, you can declare an individual test as a friend of your class by addingthis line in the class body:

   FRIEND_TEST(TestSuiteName, TestName);

  For example,

  // foo.hclass Foo { ... private: FRIEND_TEST(FooTest, BarReturnsZeroOnNull); int Bar(void* x);};// foo_test.cc...TEST(FooTest, BarReturnsZeroOnNull) { Foo foo; EXPECT_EQ(foo.Bar(NULL), 0); // Uses Foo's private member Bar().}

  Pay special attention when your class is defined in a namespace. If you wantyour test fixtures and tests to be friends of your class, then they must bedefined in the exact same namespace (no anonymous or inline namespaces).

  For example, if the code to be tested looks like:

  namespace my_namespace {class Foo { friend class FooTest; FRIEND_TEST(FooTest, Bar); FRIEND_TEST(FooTest, Baz); ... definition of the class Foo ...};} // namespace my_namespace

  Your test code should be something like:

  namespace my_namespace {class FooTest : public testing::Test { protected: ...};TEST_F(FooTest, Bar) { ... }TEST_F(FooTest, Baz) { ... }} // namespace my_namespace

“Catching” Failures

If you are building a testing utility on top of GoogleTest, you’ll want to testyour utility. What framework would you use to test it? GoogleTest, of course.

The challenge is to verify that your testing utility reports failures correctly.In frameworks that report a failure by throwing an exception, you could catchthe exception and assert on it. But GoogleTest doesn’t use exceptions, so how dowe test that a piece of code generates an expected failure?

"gtest/gtest-spi.h" contains some constructs to do this.After #including this header, you can use

 EXPECT_FATAL_FAILURE(statement, substring);

to assert that statement generates a fatal (e.g. ASSERT_*) failure in thecurrent thread whose message contains the given substring, or use

 EXPECT_NONFATAL_FAILURE(statement, substring);

if you are expecting a non-fatal (e.g. EXPECT_*) failure.

Only failures in the current thread are checked to determine the result of thistype of expectations. If statement creates new threads, failures in thesethreads are also ignored. If you want to catch failures in other threads aswell, use one of the following macros instead:

 EXPECT_FATAL_FAILURE_ON_ALL_THREADS(statement, substring); EXPECT_NONFATAL_FAILURE_ON_ALL_THREADS(statement, substring);

NOTE: Assertions from multiple threads are currently not supported on Windows.

For technical reasons, there are some caveats:

1. You cannot stream a failure message to either macro.

2. statement in EXPECT_FATAL_FAILURE{_ON_ALL_THREADS}() cannot referencelocal non-static variables or non-static members of this object.

3. statement in EXPECT_FATAL_FAILURE{_ON_ALL_THREADS}() cannot return avalue.

Registering tests programmatically

The TEST macros handle the vast majority of all use cases, but there are fewwhere runtime registration logic is required. For those cases, the frameworkprovides the ::testing::RegisterTest that allows callers to register arbitrarytests dynamically.

This is an advanced API only to be used when the TEST macros are insufficient.The macros should be preferred when possible, as they avoid most of thecomplexity of calling this function.

It provides the following signature:

template <typename Factory>TestInfo* RegisterTest(const char* test_suite_name, const char* test_name, const char* type_param, const char* value_param, const char* file, int line, Factory factory);

The factory argument is a factory callable (move-constructible) object orfunction pointer that creates a new instance of the Test object. It handlesownership to the caller. The signature of the callable is Fixture*(), whereFixture is the test fixture class for the test. All tests registered with thesame test_suite_name must return the same fixture type. This is checked atruntime.

The framework will infer the fixture class from the factory and will call theSetUpTestSuite and TearDownTestSuite for it.

Must be called before RUN_ALL_TESTS() is invoked, otherwise behavior isundefined.

Use case example:

class MyFixture : public testing::Test { public: // All of these optional, just like in regular macro usage. static void SetUpTestSuite() { ... } static void TearDownTestSuite() { ... } void SetUp() override { ... } void TearDown() override { ... }};class MyTest : public MyFixture { public: explicit MyTest(int data) : data_(data) {} void TestBody() override { ... } private: int data_;};void RegisterMyTests(const std::vector<int>& values) { for (int v : values) { testing::RegisterTest( "MyFixture", ("Test" + std::to_string(v)).c_str(), nullptr, std::to_string(v).c_str(), __FILE__, __LINE__, // Important to use the fixture type as the return type here. [=]() -> MyFixture* { return new MyTest(v); }); }}...int main(int argc, char** argv) { testing::InitGoogleTest(&argc, argv); std::vector<int> values_to_test = LoadValuesFromConfig(); RegisterMyTests(values_to_test); ... return RUN_ALL_TESTS();}

Getting the Current Test’s Name

Sometimes a function may need to know the name of the currently running test.For example, you may be using the SetUp() method of your test fixture to setthe golden file name based on which test is running. TheTestInfo class has this information.

To obtain a TestInfo object for the currently running test, callcurrent_test_info() on the UnitTestsingleton object:

 // Gets information about the currently running test. // Do NOT delete the returned object - it's managed by the UnitTest class. const testing::TestInfo* const test_info = testing::UnitTest::GetInstance()->current_test_info(); printf("We are in test %s of test suite %s.\n", test_info->name(), test_info->test_suite_name());

current_test_info() returns a null pointer if no test is running. Inparticular, you cannot find the test suite name in SetUpTestSuite(),TearDownTestSuite() (where you know the test suite name implicitly), orfunctions called from them.

Extending GoogleTest by Handling Test Events

GoogleTest provides an event listener API to let you receive notificationsabout the progress of a test program and test failures. The events you canlisten to include the start and end of the test program, a test suite, or a testmethod, among others. You may use this API to augment or replace the standardconsole output, replace the XML output, or provide a completely different formof output, such as a GUI or a database. You can also use test events ascheckpoints to implement a resource leak checker, for example.

Defining Event Listeners

To define a event listener, you subclass eithertesting::TestEventListener ortesting::EmptyTestEventListenerThe former is an (abstract) interface, where each pure virtual method can beoverridden to handle a test event (For example, when a test starts, theOnTestStart() method will be called.). The latter provides an emptyimplementation of all methods in the interface, such that a subclass only needsto override the methods it cares about.

When an event is fired, its context is passed to the handler function as anargument. The following argument types are used:

• UnitTest reflects the state of the entire test program,
• TestSuite has information about a test suite, which can contain one or moretests,
• TestInfo contains the state of a test, and
• TestPartResult represents the result of a test assertion.

An event handler function can examine the argument it receives to find outinteresting information about the event and the test program’s state.

Here’s an example:

 class MinimalistPrinter : public testing::EmptyTestEventListener { // Called before a test starts. void OnTestStart(const testing::TestInfo& test_info) override { printf("*** Test %s.%s starting.\n", test_info.test_suite_name(), test_info.name()); } // Called after a failed assertion or a SUCCESS(). void OnTestPartResult(const testing::TestPartResult& test_part_result) override { printf("%s in %s:%d\n%s\n", test_part_result.failed() ? "*** Failure" : "Success", test_part_result.file_name(), test_part_result.line_number(), test_part_result.summary()); } // Called after a test ends. void OnTestEnd(const testing::TestInfo& test_info) override { printf("*** Test %s.%s ending.\n", test_info.test_suite_name(), test_info.name()); } };

Using Event Listeners

To use the event listener you have defined, add an instance of it to theGoogleTest event listener list (represented by classTestEventListeners - note the “s”at the end of the name) in your main() function, before callingRUN_ALL_TESTS():

int main(int argc, char** argv) { testing::InitGoogleTest(&argc, argv); // Gets hold of the event listener list. testing::TestEventListeners& listeners = testing::UnitTest::GetInstance()->listeners(); // Adds a listener to the end. GoogleTest takes the ownership. listeners.Append(new MinimalistPrinter); return RUN_ALL_TESTS();}

There’s only one problem: the default test result printer is still in effect, soits output will mingle with the output from your minimalist printer. To suppressthe default printer, just release it from the event listener list and delete it.You can do so by adding one line:

 ... delete listeners.Release(listeners.default_result_printer()); listeners.Append(new MinimalistPrinter); return RUN_ALL_TESTS();

Now, sit back and enjoy a completely different output from your tests. For moredetails, see sample9_unittest.cc.

You may append more than one listener to the list. When an On*Start() orOnTestPartResult() event is fired, the listeners will receive it in the orderthey appear in the list (since new listeners are added to the end of the list,the default text printer and the default XML generator will receive the eventfirst). An On*End() event will be received by the listeners in the reverseorder. This allows output by listeners added later to be framed by output fromlisteners added earlier.

Generating Failures in Listeners

You may use failure-raising macros (EXPECT_*(), ASSERT_*(), FAIL(), etc)when processing an event. There are some restrictions:

1. You cannot generate any failure in OnTestPartResult() (otherwise it willcause OnTestPartResult() to be called recursively).
2. A listener that handles OnTestPartResult() is not allowed to generate anyfailure.

When you add listeners to the listener list, you should put listeners thathandle OnTestPartResult() before listeners that can generate failures. Thisensures that failures generated by the latter are attributed to the right testby the former.

See sample10_unittest.cc for an example of a failure-raising listener.

Running Test Programs: Advanced Options

GoogleTest test programs are ordinary executables. Once built, you can run themdirectly and affect their behavior via the following environment variablesand/or command line flags. For the flags to work, your programs must call::testing::InitGoogleTest() before calling RUN_ALL_TESTS().

To see a list of supported flags and their usage, please run your test programwith the --help flag. You can also use -h, -?, or /? for short.

If an option is specified both by an environment variable and by a flag, thelatter takes precedence.

Selecting Tests

Listing Test Names

Sometimes it is necessary to list the available tests in a program beforerunning them so that a filter may be applied if needed. Including the flag--gtest_list_tests overrides all other flags and lists tests in the followingformat:

TestSuite1. TestName1 TestName2TestSuite2. TestName

None of the tests listed are actually run if the flag is provided. There is nocorresponding environment variable for this flag.

Running a Subset of the Tests

By default, a GoogleTest program runs all tests the user has defined. Sometimes,you want to run only a subset of the tests (e.g. for debugging or quicklyverifying a change). If you set the GTEST_FILTER environment variable or the--gtest_filter flag to a filter string, GoogleTest will only run the testswhose full names (in the form of TestSuiteName.TestName) match the filter.

The format of a filter is a ‘:‘-separated list of wildcard patterns (calledthe positive patterns) optionally followed by a ‘-’ and another‘:‘-separated pattern list (called the negative patterns). A test matchesthe filter if and only if it matches any of the positive patterns but does notmatch any of the negative patterns.

A pattern may contain '*' (matches any string) or '?' (matches any singlecharacter). For convenience, the filter '*-NegativePatterns' can be alsowritten as '-NegativePatterns'.

For example:

• ./foo_test Has no flag, and thus runs all its tests.
• ./foo_test --gtest_filter=* Also runs everything, due to the singlematch-everything * value.
• ./foo_test --gtest_filter=FooTest.* Runs everything in test suiteFooTest .
• ./foo_test --gtest_filter=*Null*:*Constructor* Runs any test whose fullname contains either "Null" or "Constructor" .
• ./foo_test --gtest_filter=-*DeathTest.* Runs all non-death tests.
• ./foo_test --gtest_filter=FooTest.*-FooTest.Bar Runs everything in testsuite FooTest except FooTest.Bar.
• ./foo_test --gtest_filter=FooTest.*:BarTest.*-FooTest.Bar:BarTest.Foo Runseverything in test suite FooTest except FooTest.Bar and everything intest suite BarTest except BarTest.Foo.

Stop test execution upon first failure

By default, a GoogleTest program runs all tests the user has defined. In somecases (e.g. iterative test development & execution) it may be desirable stoptest execution upon first failure (trading improved latency for completeness).If GTEST_FAIL_FAST environment variable or --gtest_fail_fast flag is set,the test runner will stop execution as soon as the first test failure is found.

Temporarily Disabling Tests

If you have a broken test that you cannot fix right away, you can add theDISABLED_ prefix to its name. This will exclude it from execution. This isbetter than commenting out the code or using #if 0, as disabled tests arestill compiled (and thus won’t rot).

If you need to disable all tests in a test suite, you can either add DISABLED_to the front of the name of each test, or alternatively add it to the front ofthe test suite name.

For example, the following tests won’t be run by GoogleTest, even though theywill still be compiled:

// Tests that Foo does Abc.TEST(FooTest, DISABLED_DoesAbc) { ... }class DISABLED_BarTest : public testing::Test { ... };// Tests that Bar does Xyz.TEST_F(DISABLED_BarTest, DoesXyz) { ... }

NOTE: This feature should only be used for temporary pain-relief. You still haveto fix the disabled tests at a later date. As a reminder, GoogleTest will printa banner warning you if a test program contains any disabled tests.

TIP: You can easily count the number of disabled tests you have usinggrep. This number can be used as a metric forimproving your test quality.

Temporarily Enabling Disabled Tests

To include disabled tests in test execution, just invoke the test program withthe --gtest_also_run_disabled_tests flag or set theGTEST_ALSO_RUN_DISABLED_TESTS environment variable to a value other than 0.You can combine this with the --gtest_filter flag to further select whichdisabled tests to run.

Repeating the Tests

Once in a while you’ll run into a test whose result is hit-or-miss. Perhaps itwill fail only 1% of the time, making it rather hard to reproduce the bug undera debugger. This can be a major source of frustration.

The --gtest_repeat flag allows you to repeat all (or selected) test methods ina program many times. Hopefully, a flaky test will eventually fail and give youa chance to debug. Here’s how to use it:

$ foo_test --gtest_repeat=1000Repeat foo_test 1000 times and don't stop at failures.$ foo_test --gtest_repeat=-1A negative count means repeating forever.$ foo_test --gtest_repeat=1000 --gtest_break_on_failureRepeat foo_test 1000 times, stopping at the first failure. Thisis especially useful when running under a debugger: when the testfails, it will drop into the debugger and you can then inspectvariables and stacks.$ foo_test --gtest_repeat=1000 --gtest_filter=FooBar.*Repeat the tests whose name matches the filter 1000 times.

If your test program containsglobal set-up/tear-down code, it will berepeated in each iteration as well, as the flakiness may be in it. To avoidrepeating global set-up/tear-down, specify--gtest_recreate_environments_when_repeating=false{.nowrap}.

You can also specify the repeat count by setting the GTEST_REPEAT environmentvariable.

Shuffling the Tests

You can specify the --gtest_shuffle flag (or set the GTEST_SHUFFLEenvironment variable to 1) to run the tests in a program in a random order.This helps to reveal bad dependencies between tests.

By default, GoogleTest uses a random seed calculated from the current time.Therefore you’ll get a different order every time. The console output includesthe random seed value, such that you can reproduce an order-related test failurelater. To specify the random seed explicitly, use the --gtest_random_seed=SEEDflag (or set the GTEST_RANDOM_SEED environment variable), where SEED is aninteger in the range [0, 99999]. The seed value 0 is special: it tellsGoogleTest to do the default behavior of calculating the seed from the currenttime.

If you combine this with --gtest_repeat=N, GoogleTest will pick a differentrandom seed and re-shuffle the tests in each iteration.

Distributing Test Functions to Multiple Machines

If you have more than one machine you can use to run a test program, you mightwant to run the test functions in parallel and get the result faster. We callthis technique sharding, where each machine is called a shard.

GoogleTest is compatible with test sharding. To take advantage of this feature,your test runner (not part of GoogleTest) needs to do the following:

1. Allocate a number of machines (shards) to run the tests.
2. On each shard, set the GTEST_TOTAL_SHARDS environment variable to the totalnumber of shards. It must be the same for all shards.
3. On each shard, set the GTEST_SHARD_INDEX environment variable to the indexof the shard. Different shards must be assigned different indices, whichmust be in the range [0, GTEST_TOTAL_SHARDS - 1].
4. Run the same test program on all shards. When GoogleTest sees the above twoenvironment variables, it will select a subset of the test functions to run.Across all shards, each test function in the program will be run exactlyonce.
5. Wait for all shards to finish, then collect and report the results.

Your project may have tests that were written without GoogleTest and thus don’tunderstand this protocol. In order for your test runner to figure out which testsupports sharding, it can set the environment variable GTEST_SHARD_STATUS_FILEto a non-existent file path. If a test program supports sharding, it will createthis file to acknowledge that fact; otherwise it will not create it. The actualcontents of the file are not important at this time, although we may put someuseful information in it in the future.

Here’s an example to make it clear. Suppose you have a test program foo_testthat contains the following 5 test functions:

TEST(A, V)TEST(A, W)TEST(B, X)TEST(B, Y)TEST(B, Z)

Suppose you have 3 machines at your disposal. To run the test functions inparallel, you would set GTEST_TOTAL_SHARDS to 3 on all machines, and setGTEST_SHARD_INDEX to 0, 1, and 2 on the machines respectively. Then you wouldrun the same foo_test on each machine.

GoogleTest reserves the right to change how the work is distributed across theshards, but here’s one possible scenario:

• Machine #0 runs A.V and B.X.
• Machine #1 runs A.W and B.Y.
• Machine #2 runs B.Z.

Controlling Test Output

Colored Terminal Output

GoogleTest can use colors in its terminal output to make it easier to spot theimportant information:

...[----------] 1 test from FooTest[ RUN ] FooTest.DoesAbc[ OK ] FooTest.DoesAbc[----------] 2 tests from BarTest[ RUN ] BarTest.HasXyzProperty[ OK ] BarTest.HasXyzProperty[ RUN ] BarTest.ReturnsTrueOnSuccess... some error messages ...[ FAILED ] BarTest.ReturnsTrueOnSuccess...[==========] 30 tests from 14 test suites ran.[ PASSED ] 28 tests.[ FAILED ] 2 tests, listed below:[ FAILED ] BarTest.ReturnsTrueOnSuccess[ FAILED ] AnotherTest.DoesXyz 2 FAILED TESTS

You can set the GTEST_COLOR environment variable or the --gtest_colorcommand line flag to yes, no, or auto (the default) to enable colors,disable colors, or let GoogleTest decide. When the value is auto, GoogleTestwill use colors if and only if the output goes to a terminal and (on non-Windowsplatforms) the TERM environment variable is set to xterm or xterm-color.

Suppressing test passes

By default, GoogleTest prints 1 line of output for each test, indicating if itpassed or failed. To show only test failures, run the test program with--gtest_brief=1, or set the GTEST_BRIEF environment variable to 1.

Suppressing the Elapsed Time

By default, GoogleTest prints the time it takes to run each test. To disablethat, run the test program with the --gtest_print_time=0 command line flag, orset the GTEST_PRINT_TIME environment variable to 0.

Suppressing UTF-8 Text Output

In case of assertion failures, GoogleTest prints expected and actual values oftype string both as hex-encoded strings as well as in readable UTF-8 text ifthey contain valid non-ASCII UTF-8 characters. If you want to suppress the UTF-8text because, for example, you don’t have an UTF-8 compatible output medium, runthe test program with --gtest_print_utf8=0 or set the GTEST_PRINT_UTF8environment variable to 0.

Generating an XML Report

GoogleTest can emit a detailed XML report to a file in addition to its normaltextual output. The report contains the duration of each test, and thus can helpyou identify slow tests.

To generate the XML report, set the GTEST_OUTPUT environment variable or the--gtest_output flag to the string "xml:path_to_output_file", which willcreate the file at the given location. You can also just use the string "xml",in which case the output can be found in the test_detail.xml file in thecurrent directory.

If you specify a directory (for example, "xml:output/directory/" on Linux or"xml:output\directory\" on Windows), GoogleTest will create the XML file inthat directory, named after the test executable (e.g. foo_test.xml for testprogram foo_test or foo_test.exe). If the file already exists (perhaps leftover from a previous run), GoogleTest will pick a different name (e.g.foo_test_1.xml) to avoid overwriting it.

The report is based on the junitreport Ant task. Since that format wasoriginally intended for Java, a little interpretation is required to make itapply to GoogleTest tests, as shown here:

<testsuites name="AllTests" ...> <testsuite name="test_case_name" ...> <testcase name="test_name" ...> <failure message="..."/> <failure message="..."/> <failure message="..."/> </testcase> </testsuite></testsuites>

• The root <testsuites> element corresponds to the entire test program.
• <testsuite> elements correspond to GoogleTest test suites.
• <testcase> elements correspond to GoogleTest test functions.

For instance, the following program

TEST(MathTest, Addition) { ... }TEST(MathTest, Subtraction) { ... }TEST(LogicTest, NonContradiction) { ... }

could generate this report:

<?xml version="1.0" encoding="UTF-8"?><testsuites tests="3" failures="1" errors="0" time="0.035" timestamp="2011-10-31T18:52:42" name="AllTests"> <testsuite name="MathTest" tests="2" failures="1" errors="0" time="0.015"> <testcase name="Addition" file="test.cpp" line="1" status="run" time="0.007" classname=""> <failure message="Value of: add(1, 1)&#x0A; Actual: 3&#x0A;Expected: 2" type="">...</failure> <failure message="Value of: add(1, -1)&#x0A; Actual: 1&#x0A;Expected: 0" type="">...</failure> </testcase> <testcase name="Subtraction" file="test.cpp" line="2" status="run" time="0.005" classname=""> </testcase> </testsuite> <testsuite name="LogicTest" tests="1" failures="0" errors="0" time="0.005"> <testcase name="NonContradiction" file="test.cpp" line="3" status="run" time="0.005" classname=""> </testcase> </testsuite></testsuites>

Things to note:

• The tests attribute of a <testsuites> or <testsuite> element tells howmany test functions the GoogleTest program or test suite contains, while thefailures attribute tells how many of them failed.

• The time attribute expresses the duration of the test, test suite, orentire test program in seconds.

• The timestamp attribute records the local date and time of the testexecution.

• The file and line attributes record the source file location, where thetest was defined.

• Each <failure> element corresponds to a single failed GoogleTestassertion.

Generating a JSON Report

GoogleTest can also emit a JSON report as an alternative format to XML. Togenerate the JSON report, set the GTEST_OUTPUT environment variable or the--gtest_output flag to the string "json:path_to_output_file", which willcreate the file at the given location. You can also just use the string"json", in which case the output can be found in the test_detail.json filein the current directory.

The report format conforms to the following JSON Schema:

{ "$schema": "https://json-schema.org/schema#", "type": "object", "definitions": { "TestCase": { "type": "object", "properties": { "name": { "type": "string" }, "tests": { "type": "integer" }, "failures": { "type": "integer" }, "disabled": { "type": "integer" }, "time": { "type": "string" }, "testsuite": { "type": "array", "items": { "$ref": "#/definitions/TestInfo" } } } }, "TestInfo": { "type": "object", "properties": { "name": { "type": "string" }, "file": { "type": "string" }, "line": { "type": "integer" }, "status": { "type": "string", "enum": ["RUN", "NOTRUN"] }, "time": { "type": "string" }, "classname": { "type": "string" }, "failures": { "type": "array", "items": { "$ref": "#/definitions/Failure" } } } }, "Failure": { "type": "object", "properties": { "failures": { "type": "string" }, "type": { "type": "string" } } } }, "properties": { "tests": { "type": "integer" }, "failures": { "type": "integer" }, "disabled": { "type": "integer" }, "errors": { "type": "integer" }, "timestamp": { "type": "string", "format": "date-time" }, "time": { "type": "string" }, "name": { "type": "string" }, "testsuites": { "type": "array", "items": { "$ref": "#/definitions/TestCase" } } }}

The report uses the format that conforms to the following Proto3 using theJSON encoding:

syntax = "proto3";package googletest;import "google/protobuf/timestamp.proto";import "google/protobuf/duration.proto";message UnitTest { int32 tests = 1; int32 failures = 2; int32 disabled = 3; int32 errors = 4; google.protobuf.Timestamp timestamp = 5; google.protobuf.Duration time = 6; string name = 7; repeated TestCase testsuites = 8;}message TestCase { string name = 1; int32 tests = 2; int32 failures = 3; int32 disabled = 4; int32 errors = 5; google.protobuf.Duration time = 6; repeated TestInfo testsuite = 7;}message TestInfo { string name = 1; string file = 6; int32 line = 7; enum Status { RUN = 0; NOTRUN = 1; } Status status = 2; google.protobuf.Duration time = 3; string classname = 4; message Failure { string failures = 1; string type = 2; } repeated Failure failures = 5;}

For instance, the following program

TEST(MathTest, Addition) { ... }TEST(MathTest, Subtraction) { ... }TEST(LogicTest, NonContradiction) { ... }

could generate this report:

{ "tests": 3, "failures": 1, "errors": 0, "time": "0.035s", "timestamp": "2011-10-31T18:52:42Z", "name": "AllTests", "testsuites": [ { "name": "MathTest", "tests": 2, "failures": 1, "errors": 0, "time": "0.015s", "testsuite": [ { "name": "Addition", "file": "test.cpp", "line": 1, "status": "RUN", "time": "0.007s", "classname": "", "failures": [ { "message": "Value of: add(1, 1)\n Actual: 3\nExpected: 2", "type": "" }, { "message": "Value of: add(1, -1)\n Actual: 1\nExpected: 0", "type": "" } ] }, { "name": "Subtraction", "file": "test.cpp", "line": 2, "status": "RUN", "time": "0.005s", "classname": "" } ] }, { "name": "LogicTest", "tests": 1, "failures": 0, "errors": 0, "time": "0.005s", "testsuite": [ { "name": "NonContradiction", "file": "test.cpp", "line": 3, "status": "RUN", "time": "0.005s", "classname": "" } ] } ]}

IMPORTANT: The exact format of the JSON document is subject to change.

Controlling How Failures Are Reported

Detecting Test Premature Exit

Google Test implements the premature-exit-file protocol for test runners tocatch any kind of unexpected exits of test programs. Upon start, Google Testcreates the file which will be automatically deleted after all work has beenfinished. Then, the test runner can check if this file exists. In case the fileremains undeleted, the inspected test has exited prematurely.

This feature is enabled only if the TEST_PREMATURE_EXIT_FILE environmentvariable has been set.

Turning Assertion Failures into Break-Points

When running test programs under a debugger, it’s very convenient if thedebugger can catch an assertion failure and automatically drop into interactivemode. GoogleTest’s break-on-failure mode supports this behavior.

To enable it, set the GTEST_BREAK_ON_FAILURE environment variable to a valueother than 0. Alternatively, you can use the --gtest_break_on_failurecommand line flag.

Disabling Catching Test-Thrown Exceptions

GoogleTest can be used either with or without exceptions enabled. If a testthrows a C++ exception or (on Windows) a structured exception (SEH), by defaultGoogleTest catches it, reports it as a test failure, and continues with the nexttest method. This maximizes the coverage of a test run. Also, on Windows anuncaught exception will cause a pop-up window, so catching the exceptions allowsyou to run the tests automatically.

When debugging the test failures, however, you may instead want the exceptionsto be handled by the debugger, such that you can examine the call stack when anexception is thrown. To achieve that, set the GTEST_CATCH_EXCEPTIONSenvironment variable to 0, or use the --gtest_catch_exceptions=0 flag whenrunning the tests.

Sanitizer Integration

TheUndefined Behavior Sanitizer,Address Sanitizer,andThread Sanitizerall provide weak functions that you can override to trigger explicit failureswhen they detect sanitizer errors, such as creating a reference from nullptr.To override these functions, place definitions for them in a source file thatyou compile as part of your main binary:

extern "C" {void __ubsan_on_report() { FAIL() << "Encountered an undefined behavior sanitizer error";}void __asan_on_error() { FAIL() << "Encountered an address sanitizer error";}void __tsan_on_report() { FAIL() << "Encountered a thread sanitizer error";}} // extern "C"

After compiling your project with one of the sanitizers enabled, if a particulartest triggers a sanitizer error, GoogleTest will report that it failed.