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diff --git a/docs/faq.md b/docs/faq.md new file mode 100644 index 0000000..7d42ff7 --- /dev/null +++ b/docs/faq.md @@ -0,0 +1,770 @@ +# Googletest FAQ + + +## Why should test case names and test names not contain underscore? + +Underscore (`_`) is special, as C++ reserves the following to be used by the +compiler and the standard library: + +1. any identifier that starts with an `_` followed by an upper-case letter, and +1. any identifier that contains two consecutive underscores (i.e. `__`) + *anywhere* in its name. + +User code is *prohibited* from using such identifiers. + +Now let's look at what this means for `TEST` and `TEST_F`. + +Currently `TEST(TestCaseName, TestName)` generates a class named +`TestCaseName_TestName_Test`. What happens if `TestCaseName` or `TestName` +contains `_`? + +1. If `TestCaseName` starts with an `_` followed by an upper-case letter (say, + `_Foo`), we end up with `_Foo_TestName_Test`, which is reserved and thus + invalid. +1. If `TestCaseName` ends with an `_` (say, `Foo_`), we get + `Foo__TestName_Test`, which is invalid. +1. If `TestName` starts with an `_` (say, `_Bar`), we get + `TestCaseName__Bar_Test`, which is invalid. +1. If `TestName` ends with an `_` (say, `Bar_`), we get + `TestCaseName_Bar__Test`, which is invalid. + +So clearly `TestCaseName` and `TestName` cannot start or end with `_` (Actually, +`TestCaseName` can start with `_` -- as long as the `_` isn't followed by an +upper-case letter. But that's getting complicated. So for simplicity we just say +that it cannot start with `_`.). + +It may seem fine for `TestCaseName` and `TestName` to contain `_` in the middle. +However, consider this: + +```c++ +TEST(Time, Flies_Like_An_Arrow) { ... } +TEST(Time_Flies, Like_An_Arrow) { ... } +``` + +Now, the two `TEST`s will both generate the same class +(`Time_Flies_Like_An_Arrow_Test`). That's not good. + +So for simplicity, we just ask the users to avoid `_` in `TestCaseName` and +`TestName`. The rule is more constraining than necessary, but it's simple and +easy to remember. It also gives googletest some wiggle room in case its +implementation needs to change in the future. + +If you violate the rule, there may not be immediate consequences, but your test +may (just may) break with a new compiler (or a new version of the compiler you +are using) or with a new version of googletest. Therefore it's best to follow +the rule. + +## Why does googletest support `EXPECT_EQ(NULL, ptr)` and `ASSERT_EQ(NULL, ptr)` but not `EXPECT_NE(NULL, ptr)` and `ASSERT_NE(NULL, ptr)`? + +First of all you can use `EXPECT_NE(nullptr, ptr)` and `ASSERT_NE(nullptr, +ptr)`. This is the preferred syntax in the style guide because nullptr does not +have the type problems that NULL does. Which is why NULL does not work. + +Due to some peculiarity of C++, it requires some non-trivial template meta +programming tricks to support using `NULL` as an argument of the `EXPECT_XX()` +and `ASSERT_XX()` macros. Therefore we only do it where it's most needed +(otherwise we make the implementation of googletest harder to maintain and more +error-prone than necessary). + +The `EXPECT_EQ()` macro takes the *expected* value as its first argument and the +*actual* value as the second. It's reasonable that someone wants to write +`EXPECT_EQ(NULL, some_expression)`, and this indeed was requested several times. +Therefore we implemented it. + +The need for `EXPECT_NE(NULL, ptr)` isn't nearly as strong. When the assertion +fails, you already know that `ptr` must be `NULL`, so it doesn't add any +information to print `ptr` in this case. That means `EXPECT_TRUE(ptr != NULL)` +works just as well. + +If we were to support `EXPECT_NE(NULL, ptr)`, for consistency we'll have to +support `EXPECT_NE(ptr, NULL)` as well, as unlike `EXPECT_EQ`, we don't have a +convention on the order of the two arguments for `EXPECT_NE`. This means using +the template meta programming tricks twice in the implementation, making it even +harder to understand and maintain. We believe the benefit doesn't justify the +cost. + +Finally, with the growth of the gMock matcher library, we are encouraging people +to use the unified `EXPECT_THAT(value, matcher)` syntax more often in tests. One +significant advantage of the matcher approach is that matchers can be easily +combined to form new matchers, while the `EXPECT_NE`, etc, macros cannot be +easily combined. Therefore we want to invest more in the matchers than in the +`EXPECT_XX()` macros. + +## I need to test that different implementations of an interface satisfy some common requirements. Should I use typed tests or value-parameterized tests? + +For testing various implementations of the same interface, either typed tests or +value-parameterized tests can get it done. It's really up to you the user to +decide which is more convenient for you, depending on your particular case. Some +rough guidelines: + +* Typed tests can be easier to write if instances of the different + implementations can be created the same way, modulo the type. For example, + if all these implementations have a public default constructor (such that + you can write `new TypeParam`), or if their factory functions have the same + form (e.g. `CreateInstance<TypeParam>()`). +* Value-parameterized tests can be easier to write if you need different code + patterns to create different implementations' instances, e.g. `new Foo` vs + `new Bar(5)`. To accommodate for the differences, you can write factory + function wrappers and pass these function pointers to the tests as their + parameters. +* When a typed test fails, the output includes the name of the type, which can + help you quickly identify which implementation is wrong. Value-parameterized + tests cannot do this, so there you'll have to look at the iteration number + to know which implementation the failure is from, which is less direct. +* If you make a mistake writing a typed test, the compiler errors can be + harder to digest, as the code is templatized. +* When using typed tests, you need to make sure you are testing against the + interface type, not the concrete types (in other words, you want to make + sure `implicit_cast<MyInterface*>(my_concrete_impl)` works, not just that + `my_concrete_impl` works). It's less likely to make mistakes in this area + when using value-parameterized tests. + +I hope I didn't confuse you more. :-) If you don't mind, I'd suggest you to give +both approaches a try. Practice is a much better way to grasp the subtle +differences between the two tools. Once you have some concrete experience, you +can much more easily decide which one to use the next time. + +## My death tests became very slow - what happened? + +In August 2008 we had to switch the default death test style from `fast` to +`threadsafe`, as the former is no longer safe now that threaded logging is the +default. This caused many death tests to slow down. Unfortunately this change +was necessary. + +Please read [Fixing Failing Death Tests](death_test_styles.md) for what you can +do. + +## I got some run-time errors about invalid proto descriptors when using `ProtocolMessageEquals`. Help! + +**Note:** `ProtocolMessageEquals` and `ProtocolMessageEquiv` are *deprecated* +now. Please use `EqualsProto`, etc instead. + +`ProtocolMessageEquals` and `ProtocolMessageEquiv` were redefined recently and +are now less tolerant on invalid protocol buffer definitions. In particular, if +you have a `foo.proto` that doesn't fully qualify the type of a protocol message +it references (e.g. `message<Bar>` where it should be `message<blah.Bar>`), you +will now get run-time errors like: + +``` +... descriptor.cc:...] Invalid proto descriptor for file "path/to/foo.proto": +... descriptor.cc:...] blah.MyMessage.my_field: ".Bar" is not defined. +``` + +If you see this, your `.proto` file is broken and needs to be fixed by making +the types fully qualified. The new definition of `ProtocolMessageEquals` and +`ProtocolMessageEquiv` just happen to reveal your bug. + +## My death test modifies some state, but the change seems lost after the death test finishes. Why? + +Death tests (`EXPECT_DEATH`, etc) are executed in a sub-process s.t. the +expected crash won't kill the test program (i.e. the parent process). As a +result, any in-memory side effects they incur are observable in their respective +sub-processes, but not in the parent process. You can think of them as running +in a parallel universe, more or less. + +In particular, if you use [gMock](../../googlemock) and the death test statement +invokes some mock methods, the parent process will think the calls have never +occurred. Therefore, you may want to move your `EXPECT_CALL` statements inside +the `EXPECT_DEATH` macro. + +## EXPECT_EQ(htonl(blah), blah_blah) generates weird compiler errors in opt mode. Is this a googletest bug? + +Actually, the bug is in `htonl()`. + +According to `'man htonl'`, `htonl()` is a *function*, which means it's valid to +use `htonl` as a function pointer. However, in opt mode `htonl()` is defined as +a *macro*, which breaks this usage. + +Worse, the macro definition of `htonl()` uses a `gcc` extension and is *not* +standard C++. That hacky implementation has some ad hoc limitations. In +particular, it prevents you from writing `Foo<sizeof(htonl(x))>()`, where `Foo` +is a template that has an integral argument. + +The implementation of `EXPECT_EQ(a, b)` uses `sizeof(... a ...)` inside a +template argument, and thus doesn't compile in opt mode when `a` contains a call +to `htonl()`. It is difficult to make `EXPECT_EQ` bypass the `htonl()` bug, as +the solution must work with different compilers on various platforms. + +`htonl()` has some other problems as described in `//util/endian/endian.h`, +which defines `ghtonl()` to replace it. `ghtonl()` does the same thing `htonl()` +does, only without its problems. We suggest you to use `ghtonl()` instead of +`htonl()`, both in your tests and production code. + +`//util/endian/endian.h` also defines `ghtons()`, which solves similar problems +in `htons()`. + +Don't forget to add `//util/endian` to the list of dependencies in the `BUILD` +file wherever `ghtonl()` and `ghtons()` are used. The library consists of a +single header file and will not bloat your binary. + +## The compiler complains about "undefined references" to some static const member variables, but I did define them in the class body. What's wrong? + +If your class has a static data member: + +```c++ +// foo.h +class Foo { + ... + static const int kBar = 100; +}; +``` + +You also need to define it *outside* of the class body in `foo.cc`: + +```c++ +const int Foo::kBar; // No initializer here. +``` + +Otherwise your code is **invalid C++**, and may break in unexpected ways. In +particular, using it in googletest comparison assertions (`EXPECT_EQ`, etc) will +generate an "undefined reference" linker error. The fact that "it used to work" +doesn't mean it's valid. It just means that you were lucky. :-) + +## Can I derive a test fixture from another? + +Yes. + +Each test fixture has a corresponding and same named test case. This means only +one test case can use a particular fixture. Sometimes, however, multiple test +cases may want to use the same or slightly different fixtures. For example, you +may want to make sure that all of a GUI library's test cases don't leak +important system resources like fonts and brushes. + +In googletest, you share a fixture among test cases by putting the shared logic +in a base test fixture, then deriving from that base a separate fixture for each +test case that wants to use this common logic. You then use `TEST_F()` to write +tests using each derived fixture. + +Typically, your code looks like this: + +```c++ +// Defines a base test fixture. +class BaseTest : public ::testing::Test { + protected: + ... +}; + +// Derives a fixture FooTest from BaseTest. +class FooTest : public BaseTest { + protected: + void SetUp() override { + BaseTest::SetUp(); // Sets up the base fixture first. + ... additional set-up work ... + } + + void TearDown() override { + ... clean-up work for FooTest ... + BaseTest::TearDown(); // Remember to tear down the base fixture + // after cleaning up FooTest! + } + + ... functions and variables for FooTest ... +}; + +// Tests that use the fixture FooTest. +TEST_F(FooTest, Bar) { ... } +TEST_F(FooTest, Baz) { ... } + +... additional fixtures derived from BaseTest ... +``` + +If necessary, you can continue to derive test fixtures from a derived fixture. +googletest has no limit on how deep the hierarchy can be. + +For a complete example using derived test fixtures, see [googletest +sample](https://github.com/google/googletest/blob/master/googletest/samples/sample5_unittest.cc) + +## My compiler complains "void value not ignored as it ought to be." What does this mean? + +You're probably using an `ASSERT_*()` in a function that doesn't return `void`. +`ASSERT_*()` can only be used in `void` functions, due to exceptions being +disabled by our build system. Please see more details +[here](advanced.md#assertion-placement). + +## My death test hangs (or seg-faults). How do I fix it? + +In googletest, death tests are run in a child process and the way they work is +delicate. To write death tests you really need to understand how they work. +Please make sure you have read [this](advanced.md#how-it-works). + +In particular, death tests don't like having multiple threads in the parent +process. So the first thing you can try is to eliminate creating threads outside +of `EXPECT_DEATH()`. For example, you may want to use [mocks](../../googlemock) +or fake objects instead of real ones in your tests. + +Sometimes this is impossible as some library you must use may be creating +threads before `main()` is even reached. In this case, you can try to minimize +the chance of conflicts by either moving as many activities as possible inside +`EXPECT_DEATH()` (in the extreme case, you want to move everything inside), or +leaving as few things as possible in it. Also, you can try to set the death test +style to `"threadsafe"`, which is safer but slower, and see if it helps. + +If you go with thread-safe death tests, remember that they rerun the test +program from the beginning in the child process. Therefore make sure your +program can run side-by-side with itself and is deterministic. + +In the end, this boils down to good concurrent programming. You have to make +sure that there is no race conditions or dead locks in your program. No silver +bullet - sorry! + +## Should I use the constructor/destructor of the test fixture or SetUp()/TearDown()? + +The first thing to remember is that googletest does **not** reuse the same test +fixture object across multiple tests. For each `TEST_F`, googletest will create +a **fresh** test fixture object, immediately call `SetUp()`, run the test body, +call `TearDown()`, and then delete the test fixture object. + +When you need to write per-test set-up and tear-down logic, you have the choice +between using the test fixture constructor/destructor or `SetUp()/TearDown()`. +The former is usually preferred, as it has the following benefits: + +* By initializing a member variable in the constructor, we have the option to + make it `const`, which helps prevent accidental changes to its value and + makes the tests more obviously correct. +* In case we need to subclass the test fixture class, the subclass' + constructor is guaranteed to call the base class' constructor *first*, and + the subclass' destructor is guaranteed to call the base class' destructor + *afterward*. With `SetUp()/TearDown()`, a subclass may make the mistake of + forgetting to call the base class' `SetUp()/TearDown()` or call them at the + wrong time. + +You may still want to use `SetUp()/TearDown()` in the following rare cases: + +* In the body of a constructor (or destructor), it's not possible to use the + `ASSERT_xx` macros. Therefore, if the set-up operation could cause a fatal + test failure that should prevent the test from running, it's necessary to + use a `CHECK` macro or to use `SetUp()` instead of a constructor. +* If the tear-down operation could throw an exception, you must use + `TearDown()` as opposed to the destructor, as throwing in a destructor leads + to undefined behavior and usually will kill your program right away. Note + that many standard libraries (like STL) may throw when exceptions are + enabled in the compiler. Therefore you should prefer `TearDown()` if you + want to write portable tests that work with or without exceptions. +* The googletest team is considering making the assertion macros throw on + platforms where exceptions are enabled (e.g. Windows, Mac OS, and Linux + client-side), which will eliminate the need for the user to propagate + failures from a subroutine to its caller. Therefore, you shouldn't use + googletest assertions in a destructor if your code could run on such a + platform. +* In a constructor or destructor, you cannot make a virtual function call on + this object. (You can call a method declared as virtual, but it will be + statically bound.) Therefore, if you need to call a method that will be + overridden in a derived class, you have to use `SetUp()/TearDown()`. + + +## The compiler complains "no matching function to call" when I use ASSERT_PRED*. How do I fix it? + +If the predicate function you use in `ASSERT_PRED*` or `EXPECT_PRED*` is +overloaded or a template, the compiler will have trouble figuring out which +overloaded version it should use. `ASSERT_PRED_FORMAT*` and +`EXPECT_PRED_FORMAT*` don't have this problem. + +If you see this error, you might want to switch to +`(ASSERT|EXPECT)_PRED_FORMAT*`, which will also give you a better failure +message. If, however, that is not an option, you can resolve the problem by +explicitly telling the compiler which version to pick. + +For example, suppose you have + +```c++ +bool IsPositive(int n) { + return n > 0; +} + +bool IsPositive(double x) { + return x > 0; +} +``` + +you will get a compiler error if you write + +```c++ +EXPECT_PRED1(IsPositive, 5); +``` + +However, this will work: + +```c++ +EXPECT_PRED1(static_cast<bool (*)(int)>(IsPositive), 5); +``` + +(The stuff inside the angled brackets for the `static_cast` operator is the type +of the function pointer for the `int`-version of `IsPositive()`.) + +As another example, when you have a template function + +```c++ +template <typename T> +bool IsNegative(T x) { + return x < 0; +} +``` + +you can use it in a predicate assertion like this: + +```c++ +ASSERT_PRED1(IsNegative<int>, -5); +``` + +Things are more interesting if your template has more than one parameters. The +following won't compile: + +```c++ +ASSERT_PRED2(GreaterThan<int, int>, 5, 0); +``` + +as the C++ pre-processor thinks you are giving `ASSERT_PRED2` 4 arguments, which +is one more than expected. The workaround is to wrap the predicate function in +parentheses: + +```c++ +ASSERT_PRED2((GreaterThan<int, int>), 5, 0); +``` + + +## My compiler complains about "ignoring return value" when I call RUN_ALL_TESTS(). Why? + +Some people had been ignoring the return value of `RUN_ALL_TESTS()`. That is, +instead of + +```c++ + return RUN_ALL_TESTS(); +``` + +they write + +```c++ + RUN_ALL_TESTS(); +``` + +This is **wrong and dangerous**. The testing services needs to see the return +value of `RUN_ALL_TESTS()` in order to determine if a test has passed. If your +`main()` function ignores it, your test will be considered successful even if it +has a googletest assertion failure. Very bad. + +We have decided to fix this (thanks to Michael Chastain for the idea). Now, your +code will no longer be able to ignore `RUN_ALL_TESTS()` when compiled with +`gcc`. If you do so, you'll get a compiler error. + +If you see the compiler complaining about you ignoring the return value of +`RUN_ALL_TESTS()`, the fix is simple: just make sure its value is used as the +return value of `main()`. + +But how could we introduce a change that breaks existing tests? Well, in this +case, the code was already broken in the first place, so we didn't break it. :-) + +## My compiler complains that a constructor (or destructor) cannot return a value. What's going on? + +Due to a peculiarity of C++, in order to support the syntax for streaming +messages to an `ASSERT_*`, e.g. + +```c++ + ASSERT_EQ(1, Foo()) << "blah blah" << foo; +``` + +we had to give up using `ASSERT*` and `FAIL*` (but not `EXPECT*` and +`ADD_FAILURE*`) in constructors and destructors. The workaround is to move the +content of your constructor/destructor to a private void member function, or +switch to `EXPECT_*()` if that works. This +[section](advanced.md#assertion-placement) in the user's guide explains it. + +## My SetUp() function is not called. Why? + +C++ is case-sensitive. Did you spell it as `Setup()`? + +Similarly, sometimes people spell `SetUpTestCase()` as `SetupTestCase()` and +wonder why it's never called. + +## How do I jump to the line of a failure in Emacs directly? + +googletest's failure message format is understood by Emacs and many other IDEs, +like acme and XCode. If a googletest message is in a compilation buffer in +Emacs, then it's clickable. + + +## I have several test cases which share the same test fixture logic, do I have to define a new test fixture class for each of them? This seems pretty tedious. + +You don't have to. Instead of + +```c++ +class FooTest : public BaseTest {}; + +TEST_F(FooTest, Abc) { ... } +TEST_F(FooTest, Def) { ... } + +class BarTest : public BaseTest {}; + +TEST_F(BarTest, Abc) { ... } +TEST_F(BarTest, Def) { ... } +``` + +you can simply `typedef` the test fixtures: + +```c++ +typedef BaseTest FooTest; + +TEST_F(FooTest, Abc) { ... } +TEST_F(FooTest, Def) { ... } + +typedef BaseTest BarTest; + +TEST_F(BarTest, Abc) { ... } +TEST_F(BarTest, Def) { ... } +``` + +## googletest output is buried in a whole bunch of LOG messages. What do I do? + +The googletest output is meant to be a concise and human-friendly report. If +your test generates textual output itself, it will mix with the googletest +output, making it hard to read. However, there is an easy solution to this +problem. + +Since `LOG` messages go to stderr, we decided to let googletest output go to +stdout. This way, you can easily separate the two using redirection. For +example: + +```shell +$ ./my_test > gtest_output.txt +``` + + +## Why should I prefer test fixtures over global variables? + +There are several good reasons: + +1. It's likely your test needs to change the states of its global variables. + This makes it difficult to keep side effects from escaping one test and + contaminating others, making debugging difficult. By using fixtures, each + test has a fresh set of variables that's different (but with the same + names). Thus, tests are kept independent of each other. +1. Global variables pollute the global namespace. +1. Test fixtures can be reused via subclassing, which cannot be done easily + with global variables. This is useful if many test cases have something in + common. + + + ## What can the statement argument in ASSERT_DEATH() be? + +`ASSERT_DEATH(*statement*, *regex*)` (or any death assertion macro) can be used +wherever `*statement*` is valid. So basically `*statement*` can be any C++ +statement that makes sense in the current context. In particular, it can +reference global and/or local variables, and can be: + +* a simple function call (often the case), +* a complex expression, or +* a compound statement. + +Some examples are shown here: + +```c++ +// A death test can be a simple function call. +TEST(MyDeathTest, FunctionCall) { + ASSERT_DEATH(Xyz(5), "Xyz failed"); +} + +// Or a complex expression that references variables and functions. +TEST(MyDeathTest, ComplexExpression) { + const bool c = Condition(); + ASSERT_DEATH((c ? Func1(0) : object2.Method("test")), + "(Func1|Method) failed"); +} + +// Death assertions can be used any where in a function. In +// particular, they can be inside a loop. +TEST(MyDeathTest, InsideLoop) { + // Verifies that Foo(0), Foo(1), ..., and Foo(4) all die. + for (int i = 0; i < 5; i++) { + EXPECT_DEATH_M(Foo(i), "Foo has \\d+ errors", + ::testing::Message() << "where i is " << i); + } +} + +// A death assertion can contain a compound statement. +TEST(MyDeathTest, CompoundStatement) { + // Verifies that at lease one of Bar(0), Bar(1), ..., and + // Bar(4) dies. + ASSERT_DEATH({ + for (int i = 0; i < 5; i++) { + Bar(i); + } + }, + "Bar has \\d+ errors"); +} +``` + +gtest-death-test_test.cc contains more examples if you are interested. + +## I have a fixture class `FooTest`, but `TEST_F(FooTest, Bar)` gives me error ``"no matching function for call to `FooTest::FooTest()'"``. Why? + +Googletest needs to be able to create objects of your test fixture class, so it +must have a default constructor. Normally the compiler will define one for you. +However, there are cases where you have to define your own: + +* If you explicitly declare a non-default constructor for class `FooTest` + (`DISALLOW_EVIL_CONSTRUCTORS()` does this), then you need to define a + default constructor, even if it would be empty. +* If `FooTest` has a const non-static data member, then you have to define the + default constructor *and* initialize the const member in the initializer + list of the constructor. (Early versions of `gcc` doesn't force you to + initialize the const member. It's a bug that has been fixed in `gcc 4`.) + +## Why does ASSERT_DEATH complain about previous threads that were already joined? + +With the Linux pthread library, there is no turning back once you cross the line +from single thread to multiple threads. The first time you create a thread, a +manager thread is created in addition, so you get 3, not 2, threads. Later when +the thread you create joins the main thread, the thread count decrements by 1, +but the manager thread will never be killed, so you still have 2 threads, which +means you cannot safely run a death test. + +The new NPTL thread library doesn't suffer from this problem, as it doesn't +create a manager thread. However, if you don't control which machine your test +runs on, you shouldn't depend on this. + +## Why does googletest require the entire test case, instead of individual tests, to be named *DeathTest when it uses ASSERT_DEATH? + +googletest does not interleave tests from different test cases. That is, it runs +all tests in one test case first, and then runs all tests in the next test case, +and so on. googletest does this because it needs to set up a test case before +the first test in it is run, and tear it down afterwords. Splitting up the test +case would require multiple set-up and tear-down processes, which is inefficient +and makes the semantics unclean. + +If we were to determine the order of tests based on test name instead of test +case name, then we would have a problem with the following situation: + +```c++ +TEST_F(FooTest, AbcDeathTest) { ... } +TEST_F(FooTest, Uvw) { ... } + +TEST_F(BarTest, DefDeathTest) { ... } +TEST_F(BarTest, Xyz) { ... } +``` + +Since `FooTest.AbcDeathTest` needs to run before `BarTest.Xyz`, and we don't +interleave tests from different test cases, we need to run all tests in the +`FooTest` case before running any test in the `BarTest` case. This contradicts +with the requirement to run `BarTest.DefDeathTest` before `FooTest.Uvw`. + +## But I don't like calling my entire test case \*DeathTest when it contains both death tests and non-death tests. What do I do? + +You don't have to, but if you like, you may split up the test case into +`FooTest` and `FooDeathTest`, where the names make it clear that they are +related: + +```c++ +class FooTest : public ::testing::Test { ... }; + +TEST_F(FooTest, Abc) { ... } +TEST_F(FooTest, Def) { ... } + +using FooDeathTest = FooTest; + +TEST_F(FooDeathTest, Uvw) { ... EXPECT_DEATH(...) ... } +TEST_F(FooDeathTest, Xyz) { ... ASSERT_DEATH(...) ... } +``` + +## googletest prints the LOG messages in a death test's child process only when the test fails. How can I see the LOG messages when the death test succeeds? + +Printing the LOG messages generated by the statement inside `EXPECT_DEATH()` +makes it harder to search for real problems in the parent's log. Therefore, +googletest only prints them when the death test has failed. + +If you really need to see such LOG messages, a workaround is to temporarily +break the death test (e.g. by changing the regex pattern it is expected to +match). Admittedly, this is a hack. We'll consider a more permanent solution +after the fork-and-exec-style death tests are implemented. + +## The compiler complains about "no match for 'operator<<'" when I use an assertion. What gives? + +If you use a user-defined type `FooType` in an assertion, you must make sure +there is an `std::ostream& operator<<(std::ostream&, const FooType&)` function +defined such that we can print a value of `FooType`. + +In addition, if `FooType` is declared in a name space, the `<<` operator also +needs to be defined in the *same* name space. See go/totw/49 for details. + +## How do I suppress the memory leak messages on Windows? + +Since the statically initialized googletest singleton requires allocations on +the heap, the Visual C++ memory leak detector will report memory leaks at the +end of the program run. The easiest way to avoid this is to use the +`_CrtMemCheckpoint` and `_CrtMemDumpAllObjectsSince` calls to not report any +statically initialized heap objects. See MSDN for more details and additional +heap check/debug routines. + + +## How can my code detect if it is running in a test? + +If you write code that sniffs whether it's running in a test and does different +things accordingly, you are leaking test-only logic into production code and +there is no easy way to ensure that the test-only code paths aren't run by +mistake in production. Such cleverness also leads to +[Heisenbugs](https://en.wikipedia.org/wiki/Heisenbug). Therefore we strongly +advise against the practice, and googletest doesn't provide a way to do it. + +In general, the recommended way to cause the code to behave differently under +test is [Dependency Injection](https://en.wikipedia.org/wiki/Dependency_injection). You can inject +different functionality from the test and from the production code. Since your +production code doesn't link in the for-test logic at all (the +[`testonly`](https://docs.bazel.build/versions/master/be/common-definitions.html#common.testonly) +attribute for BUILD targets helps to ensure that), there is no danger in +accidentally running it. + +However, if you *really*, *really*, *really* have no choice, and if you follow +the rule of ending your test program names with `_test`, you can use the +*horrible* hack of sniffing your executable name (`argv[0]` in `main()`) to know +whether the code is under test. + + +## How do I temporarily disable a test? + +If you have a broken test that you cannot fix right away, you can add the +DISABLED_ prefix to its name. This will exclude it from execution. This is +better than commenting out the code or using #if 0, as disabled tests are still +compiled (and thus won't rot). + +To include disabled tests in test execution, just invoke the test program with +the --gtest_also_run_disabled_tests flag. + +## Is it OK if I have two separate `TEST(Foo, Bar)` test methods defined in different namespaces? + +Yes. + +The rule is **all test methods in the same test case must use the same fixture +class.** This means that the following is **allowed** because both tests use the +same fixture class (`::testing::Test`). + +```c++ +namespace foo { +TEST(CoolTest, DoSomething) { + SUCCEED(); +} +} // namespace foo + +namespace bar { +TEST(CoolTest, DoSomething) { + SUCCEED(); +} +} // namespace bar +``` + +However, the following code is **not allowed** and will produce a runtime error +from googletest because the test methods are using different test fixture +classes with the same test case name. + +```c++ +namespace foo { +class CoolTest : public ::testing::Test {}; // Fixture foo::CoolTest +TEST_F(CoolTest, DoSomething) { + SUCCEED(); +} +} // namespace foo + +namespace bar { +class CoolTest : public ::testing::Test {}; // Fixture: bar::CoolTest +TEST_F(CoolTest, DoSomething) { + SUCCEED(); +} +} // namespace bar +``` |