Subversion Repositories s80186

If you cannot find the answer to your question here, and you have read

[Primer](Primer.md) and [AdvancedGuide](AdvancedGuide.md), send it to

googletestframework@googlegroups.com.

## Why should I use Google Test instead of my favorite C++ testing framework? ##

First, let us say clearly that we don't want to get into the debate of

which C++ testing framework is **the best**.  There exist many fine

frameworks for writing C++ tests, and we have tremendous respect for

the developers and users of them.  We don't think there is (or will

be) a single best framework - you have to pick the right tool for the

particular task you are tackling.

We created Google Test because we couldn't find the right combination

of features and conveniences in an existing framework to satisfy _our_

needs.  The following is a list of things that _we_ like about Google

Test.  We don't claim them to be unique to Google Test - rather, the

combination of them makes Google Test the choice for us.  We hope this

list can help you decide whether it is for you too.

  * Google Test is designed to be portable: it doesn't require exceptions or RTTI; it works around various bugs in various compilers and environments; etc.  As a result, it works on Linux, Mac OS X, Windows and several embedded operating systems.

  * Nonfatal assertions (`EXPECT_*`) have proven to be great time savers, as they allow a test to report multiple failures in a single edit-compile-test cycle.

  * It's easy to write assertions that generate informative messages: you just use the stream syntax to append any additional information, e.g. `ASSERT_EQ(5, Foo(i)) << " where i = " << i;`.  It doesn't require a new set of macros or special functions.

  * Google Test automatically detects your tests and doesn't require you to enumerate them in order to run them.

  * Death tests are pretty handy for ensuring that your asserts in production code are triggered by the right conditions.

  * `SCOPED_TRACE` helps you understand the context of an assertion failure when it comes from inside a sub-routine or loop.

  * You can decide which tests to run using name patterns.  This saves time when you want to quickly reproduce a test failure.

  * Google Test can generate XML test result reports that can be parsed by popular continuous build system like Hudson.

  * Simple things are easy in Google Test, while hard things are possible: in addition to advanced features like [global test environments](AdvancedGuide.md#global-set-up-and-tear-down) and tests parameterized by [values](AdvancedGuide.md#value-parameterized-tests) or [types](docs/AdvancedGuide.md#typed-tests), Google Test supports various ways for the user to extend the framework -- if Google Test doesn't do something out of the box, chances are that a user can implement the feature using Google Test's public API, without changing Google Test itself.  In particular, you can:

    * expand your testing vocabulary by defining [custom predicates](AdvancedGuide.md#predicate-assertions-for-better-error-messages),

    * teach Google Test how to [print your types](AdvancedGuide.md#teaching-google-test-how-to-print-your-values),

    * define your own testing macros or utilities and verify them using Google Test's [Service Provider Interface](AdvancedGuide.md#catching-failures), and

    * reflect on the test cases or change the test output format by intercepting the [test events](AdvancedGuide.md#extending-google-test-by-handling-test-events).

## I'm getting warnings when compiling Google Test.  Would you fix them? ##

We strive to minimize compiler warnings Google Test generates.  Before releasing a new version, we test to make sure that it doesn't generate warnings when compiled using its CMake script on Windows, Linux, and Mac OS.

Unfortunately, this doesn't mean you are guaranteed to see no warnings when compiling Google Test in your environment:

  * You may be using a different compiler as we use, or a different version of the same compiler.  We cannot possibly test for all compilers.

  * You may be compiling on a different platform as we do.

  * Your project may be using different compiler flags as we do.

It is not always possible to make Google Test warning-free for everyone.  Or, it may not be desirable if the warning is rarely enabled and fixing the violations makes the code more complex.

If you see warnings when compiling Google Test, we suggest that you use the `-isystem` flag (assuming your are using GCC) to mark Google Test headers as system headers.  That'll suppress warnings from Google Test headers.

## Why should not test case names and test names 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 containers 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:

``` cpp

TEST(Time, Flies_Like_An_Arrow) { ... }

TEST(Time_Flies, Like_An_Arrow) { ... }

```

Now, the two `TEST`s will both generate the same class

(`Time_Files_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 Google Test some wiggle

room in case its implementation needs to change in the future.

If you violate the rule, there may not be immediately 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 Google

Test.  Therefore it's best to follow the rule.

## Why is it not recommended to install a pre-compiled copy of Google Test (for example, into /usr/local)? ##

In the early days, we said that you could install

compiled Google Test libraries on `*`nix systems using `make install`.

Then every user of your machine can write tests without

recompiling Google Test.

This seemed like a good idea, but it has a

got-cha: every user needs to compile his tests using the _same_ compiler

flags used to compile the installed Google Test libraries; otherwise

he may run into undefined behaviors (i.e. the tests can behave

strangely and may even crash for no obvious reasons).

Why?  Because C++ has this thing called the One-Definition Rule: if

two C++ source files contain different definitions of the same

class/function/variable, and you link them together, you violate the

rule.  The linker may or may not catch the error (in many cases it's

not required by the C++ standard to catch the violation).  If it

doesn't, you get strange run-time behaviors that are unexpected and

hard to debug.

If you compile Google Test and your test code using different compiler

flags, they may see different definitions of the same

class/function/variable (e.g. due to the use of `#if` in Google Test).

Therefore, for your sanity, we recommend to avoid installing pre-compiled

Google Test libraries.  Instead, each project should compile

Google Test itself such that it can be sure that the same flags are

used for both Google Test and the tests.

## How do I generate 64-bit binaries on Windows (using Visual Studio 2008)? ##

(Answered by Trevor Robinson)

Load the supplied Visual Studio solution file, either `msvc\gtest-md.sln` or

`msvc\gtest.sln`. Go through the migration wizard to migrate the

solution and project files to Visual Studio 2008. Select

`Configuration Manager...` from the `Build` menu. Select `` from

the `Active solution platform` dropdown.  Select `x64` from the new

platform dropdown, leave `Copy settings from` set to `Win32` and

`Create new project platforms` checked, then click `OK`. You now have

`Win32` and `x64` platform configurations, selectable from the

`Standard` toolbar, which allow you to toggle between building 32-bit or

64-bit binaries (or both at once using Batch Build).

In order to prevent build output files from overwriting one another,

you'll need to change the `Intermediate Directory` settings for the

newly created platform configuration across all the projects. To do

this, multi-select (e.g. using shift-click) all projects (but not the

solution) in the `Solution Explorer`. Right-click one of them and

select `Properties`. In the left pane, select `Configuration Properties`,

and from the `Configuration` dropdown, select `All Configurations`.

Make sure the selected platform is `x64`. For the

`Intermediate Directory` setting, change the value from

`$(PlatformName)\$(ConfigurationName)` to

`$(OutDir)\$(ProjectName)`. Click `OK` and then build the

solution. When the build is complete, the 64-bit binaries will be in

the `msvc\x64\Debug` directory.

## Can I use Google Test on MinGW? ##

We haven't tested this ourselves, but Per Abrahamsen reported that he

was able to compile and install Google Test successfully when using

MinGW from Cygwin.  You'll need to configure it with:

`PATH/TO/configure CC="gcc -mno-cygwin" CXX="g++ -mno-cygwin"`

You should be able to replace the `-mno-cygwin` option with direct links

to the real MinGW binaries, but we haven't tried that.

Caveats:

  * There are many warnings when compiling.

  * `make check` will produce some errors as not all tests for Google Test itself are compatible with MinGW.

We also have reports on successful cross compilation of Google Test

MinGW binaries on Linux using

[these instructions](http://wiki.wxwidgets.org/Cross-Compiling_Under_Linux#Cross-compiling_under_Linux_for_MS_Windows)

on the WxWidgets site.

Please contact `googletestframework@googlegroups.com` if you are

interested in improving the support for MinGW.

## Why does Google Test support EXPECT\_EQ(NULL, ptr) and ASSERT\_EQ(NULL, ptr) but not EXPECT\_NE(NULL, ptr) and ASSERT\_NE(NULL, ptr)? ##

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 Google Test

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 Google Mock's [matcher](../../googlemock/docs/CookBook.md#using-matchers-in-google-test-assertions) 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.

## Does Google Test support running tests in parallel? ##

Test runners tend to be tightly coupled with the build/test

environment, and Google Test doesn't try to solve the problem of

running tests in parallel.  Instead, we tried to make Google Test work

nicely with test runners.  For example, Google Test's XML report

contains the time spent on each test, and its `gtest_list_tests` and

`gtest_filter` flags can be used for splitting the execution of test

methods into multiple processes.  These functionalities can help the

test runner run the tests in parallel.

## Why don't Google Test run the tests in different threads to speed things up? ##

It's difficult to write thread-safe code.  Most tests are not written

with thread-safety in mind, and thus may not work correctly in a

multi-threaded setting.

If you think about it, it's already hard to make your code work when

you know what other threads are doing.  It's much harder, and

sometimes even impossible, to make your code work when you don't know

what other threads are doing (remember that test methods can be added,

deleted, or modified after your test was written).  If you want to run

the tests in parallel, you'd better run them in different processes.

## Why aren't Google Test assertions implemented using exceptions? ##

Our original motivation was to be able to use Google Test in projects

that disable exceptions.  Later we realized some additional benefits

of this approach:

  1. Throwing in a destructor is undefined behavior in C++.  Not using exceptions means Google Test's assertions are safe to use in destructors.

  1. The `EXPECT_*` family of macros will continue even after a failure, allowing multiple failures in a `TEST` to be reported in a single run. This is a popular feature, as in C++ the edit-compile-test cycle is usually quite long and being able to fixing more than one thing at a time is a blessing.

  1. If assertions are implemented using exceptions, a test may falsely ignore a failure if it's caught by user code:

``` cpp

try { ... ASSERT_TRUE(...) ... }

catch (...) { ... }

```

The above code will pass even if the `ASSERT_TRUE` throws.  While it's unlikely for someone to write this in a test, it's possible to run into this pattern when you write assertions in callbacks that are called by the code under test.

The downside of not using exceptions is that `ASSERT_*` (implemented

using `return`) will only abort the current function, not the current

`TEST`.

## Why do we use two different macros for tests with and without fixtures? ##

Unfortunately, C++'s macro system doesn't allow us to use the same

macro for both cases.  One possibility is to provide only one macro

for tests with fixtures, and require the user to define an empty

fixture sometimes:

``` cpp

class FooTest : public ::testing::Test {};

TEST_F(FooTest, DoesThis) { ... }

```

or

``` cpp

typedef ::testing::Test FooTest;

TEST_F(FooTest, DoesThat) { ... }

```

Yet, many people think this is one line too many. :-) Our goal was to

make it really easy to write tests, so we tried to make simple tests

trivial to create.  That means using a separate macro for such tests.

We think neither approach is ideal, yet either of them is reasonable.

In the end, it probably doesn't matter much either way.

## Why don't we use structs as test fixtures? ##

We like to use structs only when representing passive data.  This

distinction between structs and classes is good for documenting the

intent of the code's author.  Since test fixtures have logic like

`SetUp()` and `TearDown()`, they are better defined as classes.

## Why are death tests implemented as assertions instead of using a test runner? ##

Our goal was to make death tests as convenient for a user as C++

possibly allows.  In particular:

  * The runner-style requires to split the information into two pieces: the definition of the death test itself, and the specification for the runner on how to run the death test and what to expect.  The death test would be written in C++, while the runner spec may or may not be.  A user needs to carefully keep the two in sync. `ASSERT_DEATH(statement, expected_message)` specifies all necessary information in one place, in one language, without boilerplate code. It is very declarative.

  * `ASSERT_DEATH` has a similar syntax and error-reporting semantics as other Google Test assertions, and thus is easy to learn.

  * `ASSERT_DEATH` can be mixed with other assertions and other logic at your will.  You are not limited to one death test per test method. For example, you can write something like:

``` cpp

    if (FooCondition()) {

      ASSERT_DEATH(Bar(), "blah");

    } else {

      ASSERT_EQ(5, Bar());

    }

```

If you prefer one death test per test method, you can write your tests in that style too, but we don't want to impose that on the users.  The fewer artificial limitations the better.

  * `ASSERT_DEATH` can reference local variables in the current function, and you can decide how many death tests you want based on run-time information.  For example,

``` cpp

    const int count = GetCount();  // Only known at run time.

    for (int i = 1; i <= count; i++) {

      ASSERT_DEATH({

        double* buffer = new double[i];

        ... initializes buffer ...

        Foo(buffer, i)

      }, "blah blah");

    }

```

The runner-based approach tends to be more static and less flexible, or requires more user effort to get this kind of flexibility.

Another interesting thing about `ASSERT_DEATH` is that it calls `fork()`

to create a child process to run the death test.  This is lightening

fast, as `fork()` uses copy-on-write pages and incurs almost zero

overhead, and the child process starts from the user-supplied

statement directly, skipping all global and local initialization and

any code leading to the given statement.  If you launch the child

process from scratch, it can take seconds just to load everything and

start running if the test links to many libraries dynamically.

## 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.

## 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:

``` cpp

// foo.h

class Foo {

  ...

  static const int kBar = 100;

};

```

You also need to define it _outside_ of the class body in `foo.cc`:

``` cpp

const int Foo::kBar;  // No initializer here.

```

Otherwise your code is **invalid C++**, and may break in unexpected ways. In

particular, using it in Google Test comparison assertions (`EXPECT_EQ`, etc)

will generate an "undefined reference" linker error.

## I have an interface that has several implementations. Can I write a set of tests once and repeat them over all the implementations? ##

Google Test doesn't yet have good support for this kind of tests, or

data-driven tests in general. We hope to be able to make improvements in this

area soon.

## 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 Google Test, 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:

``` cpp

// Defines a base test fixture.

class BaseTest : public ::testing::Test {

  protected:

   ...

};

// Derives a fixture FooTest from BaseTest.

class FooTest : public BaseTest {

  protected:

    virtual void SetUp() {

      BaseTest::SetUp();  // Sets up the base fixture first.

      ... additional set-up work ...

    }

    virtual void TearDown() {

      ... 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.

Google Test has no limit on how deep the hierarchy can be.

For a complete example using derived test fixtures, see

[sample5](../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.

## My death test hangs (or seg-faults). How do I fix it? ##

In Google Test, 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.

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()`.

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 the set-up/tear-down function? ##

The first thing to remember is that Google Test does not reuse the

same test fixture object across multiple tests. For each `TEST_F`,

Google Test will create a fresh test fixture object, _immediately_

call `SetUp()`, run the test body, call `TearDown()`, and then

_immediately_ 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 moment.

You may still want to use `SetUp()/TearDown()` in the following rare cases:

  * 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 assertion macros throw an exception when flag `--gtest_throw_on_failure` is specified. Therefore, you shouldn't use Google Test assertions in a destructor if you plan to run your tests with this flag.

  * 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 overriden in a derived class, you have to use `SetUp()/TearDown()`.

## The compiler complains "no matching function to call" when I use ASSERT\_PREDn. 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

``` cpp

bool IsPositive(int n) {

  return n > 0;

}

bool IsPositive(double x) {

  return x > 0;

}

```

you will get a compiler error if you write

``` cpp

EXPECT_PRED1(IsPositive, 5);

```

However, this will work:

``` cpp

EXPECT_PRED1(*static_cast*(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

``` cpp

template 

bool IsNegative(T x) {

  return x < 0;

}

```

you can use it in a predicate assertion like this:

``` cpp

ASSERT_PRED1(IsNegative**, -5);

```

Things are more interesting if your template has more than one parameters. The

following won't compile:

``` cpp

ASSERT_PRED2(*GreaterThan*, 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:

``` cpp

ASSERT_PRED2(*(GreaterThan)*, 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

``` cpp

return RUN_ALL_TESTS();

```

they write

``` cpp

RUN_ALL_TESTS();

```

This is wrong and dangerous. A test runner 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

Google Test assertion failure. Very bad.

To help the users avoid this dangerous bug, the implementation of

`RUN_ALL_TESTS()` causes gcc to raise this warning, when the return value is

ignored. If you see this warning, the fix is simple: just make sure its value

is used as the return value of `main()`.

## 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.

``` cpp

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 in the user's guide explains

it.

## My set-up function is not called. Why? ##

C++ is case-sensitive. It should be spelled as `SetUp()`.  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? ##

Google Test's failure message format is understood by Emacs and many other

IDEs, like acme and XCode. If a Google Test message is in a compilation buffer

in Emacs, then it's clickable. You can now hit `enter` on a message to jump to

the corresponding source code, or use `C-x `` to jump to the next failure.

## 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

``` cpp

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:

``` cpp

typedef BaseTest FooTest;

TEST_F(FooTest, Abc) { ... }

TEST_F(FooTest, Def) { ... }

typedef BaseTest BarTest;

TEST_F(BarTest, Abc) { ... }

TEST_F(BarTest, Def) { ... }

```

## The Google Test output is buried in a whole bunch of log messages. What do I do? ##

The Google Test output is meant to be a concise and human-friendly report. If

your test generates textual output itself, it will mix with the Google Test

output, making it hard to read. However, there is an easy solution to this

problem.

Since most log messages go to stderr, we decided to let Google Test output go

to stdout. This way, you can easily separate the two using redirection. For

example:

```

./my_test > googletest_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.

## How do I test private class members without writing FRIEND\_TEST()s? ##

You should try to write testable code, which means classes should be easily

tested from their public interface. One way to achieve this is the Pimpl idiom:

you move all private members of a class into a helper class, and make all

members of the helper class public.

You have several other options that don't require using `FRIEND_TEST`:

  * Write the tests as members of the fixture class:

``` cpp

class Foo {

  friend class FooTest;

  ...

};

class FooTest : public ::testing::Test {

 protected:

  ...

  void Test1() {...} // This accesses private members of class Foo.

  void Test2() {...} // So does this one.

};

TEST_F(FooTest, Test1) {

  Test1();

}

TEST_F(FooTest, Test2) {

  Test2();

}

```

  * In the fixture class, write accessors for the tested class' private members, then use the accessors in your tests:

``` cpp

class Foo {

  friend class FooTest;

  ...

};

class FooTest : public ::testing::Test {

 protected:

  ...

  T1 get_private_member1(Foo* obj) {

    return obj->private_member1_;

  }

};

TEST_F(FooTest, Test1) {

  ...

  get_private_member1(x)

  ...

}

```

  * If the methods are declared **protected**, you can change their access level in a test-only subclass:

``` cpp

class YourClass {

  ...

 protected: // protected access for testability.

  int DoSomethingReturningInt();

  ...

};

// in the your_class_test.cc file:

class TestableYourClass : public YourClass {

  ...

 public: using YourClass::DoSomethingReturningInt; // changes access rights

  ...

};

TEST_F(YourClassTest, DoSomethingTest) {

  TestableYourClass obj;

  assertEquals(expected_value, obj.DoSomethingReturningInt());

}

```

## How do I test private class static members without writing FRIEND\_TEST()s? ##

We find private static methods clutter the header file.  They are

implementation details and ideally should be kept out of a .h. So often I make

them free functions instead.

Instead of:

``` cpp

// foo.h

class Foo {

  ...

 private:

  static bool Func(int n);

};

// foo.cc

bool Foo::Func(int n) { ... }

// foo_test.cc

EXPECT_TRUE(Foo::Func(12345));

```

You probably should better write:

``` cpp

// foo.h

class Foo {

  ...

};

// foo.cc

namespace internal {

  bool Func(int n) { ... }

}

// foo_test.cc

namespace internal {

  bool Func(int n);

}

EXPECT_TRUE(internal::Func(12345));

```

## I would like to run a test several times with different parameters. Do I need to write several similar copies of it? ##

No. You can use a feature called [value-parameterized tests](AdvancedGuide.md#Value_Parameterized_Tests) which

lets you repeat your tests with different parameters, without defining it more than once.

## How do I test a file that defines main()? ##

To test a `foo.cc` file, you need to compile and link it into your unit test

program. However, when the file contains a definition for the `main()`

function, it will clash with the `main()` of your unit test, and will result in

a build error.

The right solution is to split it into three files:

  1. `foo.h` which contains the declarations,

  1. `foo.cc` which contains the definitions except `main()`, and

  1. `foo_main.cc` which contains nothing but the definition of `main()`.

Then `foo.cc` can be easily tested.

If you are adding tests to an existing file and don't want an intrusive change

like this, there is a hack: just include the entire `foo.cc` file in your unit

test. For example:

``` cpp

// File foo_unittest.cc

// The headers section

...

// Renames main() in foo.cc to make room for the unit test main()

#define main FooMain

#include "a/b/foo.cc"

// The tests start here.

...

```

However, please remember this is a hack and should only be used as the last

resort.

## 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:

``` cpp

// 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");}

```

`googletest_unittest.cc` contains more examples if you are interested.

## What syntax does the regular expression in ASSERT\_DEATH use? ##

On POSIX systems, Google Test uses the POSIX Extended regular

expression syntax

(http://en.wikipedia.org/wiki/Regular_expression#POSIX_Extended_Regular_Expressions).

On Windows, it uses a limited variant of regular expression

syntax. For more details, see the

[regular expression syntax](AdvancedGuide.md#Regular_Expression_Syntax).

## I have a fixture class Foo, but TEST\_F(Foo, Bar) gives me error "no matching function for call to Foo::Foo()". Why? ##

Google Test 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 `Foo`, then you need to define a default constructor, even if it would be empty.

  * If `Foo` 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 Google Test require the entire test case, instead of individual tests, to be named FOODeathTest when it uses ASSERT\_DEATH? ##

Google Test 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. Google Test 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:

``` cpp

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 FOODeathTest 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:

``` cpp

class FooTest : public ::testing::Test { ... };

TEST_F(FooTest, Abc) { ... }

TEST_F(FooTest, Def) { ... }

typedef FooTest FooDeathTest;

TEST_F(FooDeathTest, Uvw) { ... EXPECT_DEATH(...) ... }

TEST_F(FooDeathTest, Xyz) { ... ASSERT_DEATH(...) ... }

```

## 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.

## How do I suppress the memory leak messages on Windows? ##

Since the statically initialized Google Test 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.

## I am building my project with Google Test in Visual Studio and all I'm getting is a bunch of linker errors (or warnings). Help! ##

You may get a number of the following linker error or warnings if you