Now that you have read [Primer](Primer.md) and learned how to write tests

using Google Test, it's time to learn some new tricks. This document

will show you more assertions as well as how to construct complex

failure messages, propagate fatal failures, reuse and speed up your

test fixtures, and use various flags with your tests.

# More Assertions #

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

assertions.

## Explicit Success and Failure ##

These three assertions do not actually test a value or expression. Instead,

they generate a success or failure directly. Like the macros that actually

perform a test, you may stream a custom failure message into the them.

| `SUCCEED();` |

|:-------------|

Generates a success. This does NOT make the overall test succeed. A test is

considered successful only if none of its assertions fail during its execution.

Note: `SUCCEED()` is purely documentary and currently doesn't generate any

user-visible output. However, we may add `SUCCEED()` messages to Google Test's

output in the future.

| `FAIL();`  | `ADD_FAILURE();` | `ADD_FAILURE_AT("`_file\_path_`", `_line\_number_`);` |

|:-----------|:-----------------|:------------------------------------------------------|

`FAIL()` generates a fatal failure, while `ADD_FAILURE()` and `ADD_FAILURE_AT()` generate a nonfatal

failure. These are useful when control flow, rather than a Boolean expression,

deteremines the test's success or failure. For example, you might want to write

something like:

```

switch(expression) {

  case 1: ... some checks ...

  case 2: ... some other checks

  ...

  default: FAIL() << "We shouldn't get here.";

}

```

Note: you can only use `FAIL()` in functions that return `void`. See the [Assertion Placement section](#assertion-placement) for more information.

_Availability_: Linux, Windows, Mac.

## Exception Assertions ##

These are for verifying that a piece of code throws (or does not

throw) an exception of the given type:

| **Fatal assertion** | **Nonfatal assertion** | **Verifies** |

|:--------------------|:-----------------------|:-------------|

| `ASSERT_THROW(`_statement_, _exception\_type_`);`  | `EXPECT_THROW(`_statement_, _exception\_type_`);`  | _statement_ throws an exception of the given type  |

| `ASSERT_ANY_THROW(`_statement_`);`                | `EXPECT_ANY_THROW(`_statement_`);`                | _statement_ throws an exception of any type        |

| `ASSERT_NO_THROW(`_statement_`);`                 | `EXPECT_NO_THROW(`_statement_`);`                 | _statement_ doesn't throw any exception            |

Examples:

```

ASSERT_THROW(Foo(5), bar_exception);

EXPECT_NO_THROW({

  int n = 5;

  Bar(&n);

});

```

_Availability_: Linux, Windows, Mac; since version 1.1.0.

## Predicate Assertions for Better Error Messages ##

Even though Google Test has a rich set of assertions, they can never be

complete, as it's impossible (nor a good idea) to anticipate all the scenarios

a user might run into. Therefore, sometimes a user has to use `EXPECT_TRUE()`

to check a complex expression, for lack of a better macro. This has the problem

of not showing you the values of the parts of the expression, making it hard to

understand what went wrong. As a workaround, some users choose to construct the

failure message by themselves, streaming it into `EXPECT_TRUE()`. However, this

is awkward especially when the expression has side-effects or is expensive to

evaluate.

Google Test gives you three different options to solve this problem:

### Using an Existing Boolean Function ###

If you already have a function or a functor that returns `bool` (or a type

that can be implicitly converted to `bool`), you can use it in a _predicate

assertion_ to get the function arguments printed for free:

| **Fatal assertion** | **Nonfatal assertion** | **Verifies** |

|:--------------------|:-----------------------|:-------------|

| `ASSERT_PRED1(`_pred1, val1_`);`       | `EXPECT_PRED1(`_pred1, val1_`);` | _pred1(val1)_ returns true |

| `ASSERT_PRED2(`_pred2, val1, val2_`);` | `EXPECT_PRED2(`_pred2, val1, val2_`);` |  _pred2(val1, val2)_ returns true |

|  ...                | ...                    | ...          |

In the above, _predn_ is an _n_-ary predicate function or functor, where

_val1_, _val2_, ..., and _valn_ are its arguments. The assertion succeeds

if the predicate returns `true` when applied to the given arguments, and fails

otherwise. When the assertion fails, it prints the value of each argument. In

either case, the arguments are evaluated exactly once.

Here's an example. Given

```

// Returns true iff m and n have no common divisors except 1.

bool MutuallyPrime(int m, int n) { ... }

const int a = 3;

const int b = 4;

const int c = 10;

```

the assertion `EXPECT_PRED2(MutuallyPrime, a, b);` will succeed, while the

assertion `EXPECT_PRED2(MutuallyPrime, b, c);` will fail with the message

!MutuallyPrime(b, c) is false, where

b is 4

c is 10

**Notes:**

  1. If you see a compiler error "no matching function to call" when using `ASSERT_PRED*` or `EXPECT_PRED*`, please see [this FAQ](FAQ.md#the-compiler-complains-no-matching-function-to-call-when-i-use-assert_predn-how-do-i-fix-it) for how to resolve it.

  1. Currently we only provide predicate assertions of arity <= 5. If you need a higher-arity assertion, let us know.

_Availability_: Linux, Windows, Mac

### Using a Function That Returns an AssertionResult ###

While `EXPECT_PRED*()` and friends are handy for a quick job, the

syntax is not satisfactory: you have to use different macros for

different arities, and it feels more like Lisp than C++.  The

`::testing::AssertionResult` class solves this problem.

An `AssertionResult` object represents the result of an assertion

(whether it's a success or a failure, and an associated message).  You

can create an `AssertionResult` 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

`AssertionResult` object.

To provide more readable messages in Boolean assertions

(e.g. `EXPECT_TRUE()`), write a predicate function that returns

`AssertionResult` instead of `bool`. For example, 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: false

Expected: true

If you want informative messages in `EXPECT_FALSE` and `ASSERT_FALSE`

as well, and are fine with making the predicate slower in the success

case, you can supply a success 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

_Availability_: Linux, Windows, Mac; since version 1.4.1.

### Using a Predicate-Formatter ###

If you find the default message generated by `(ASSERT|EXPECT)_PRED*` and

`(ASSERT|EXPECT)_(TRUE|FALSE)` unsatisfactory, or some arguments to your

predicate do not support streaming to `ostream`, you can instead use the

following _predicate-formatter assertions_ to _fully_ customize how the

message is formatted:

| **Fatal assertion** | **Nonfatal assertion** | **Verifies** |

|:--------------------|:-----------------------|:-------------|

| `ASSERT_PRED_FORMAT1(`_pred\_format1, val1_`);`        | `EXPECT_PRED_FORMAT1(`_pred\_format1, val1_`);` | _pred\_format1(val1)_ is successful |

| `ASSERT_PRED_FORMAT2(`_pred\_format2, val1, val2_`);` | `EXPECT_PRED_FORMAT2(`_pred\_format2, val1, val2_`);` | _pred\_format2(val1, val2)_ is successful |

| `...`               | `...`                  | `...`        |

The difference between this and the previous two groups of macros is that instead of

a predicate, `(ASSERT|EXPECT)_PRED_FORMAT*` take a _predicate-formatter_

(_pred\_formatn_), which is a function or functor with the signature:

`::testing::AssertionResult PredicateFormattern(const char* `_expr1_`, const char* `_expr2_`, ... const char* `_exprn_`, T1 `_val1_`, T2 `_val2_`, ... Tn `_valn_`);`

where _val1_, _val2_, ..., and _valn_ are the values of the predicate

arguments, and _expr1_, _expr2_, ..., and _exprn_ are the corresponding

expressions as they appear in the source code. The types `T1`, `T2`, ..., and

`Tn` can be either value types or reference types. For example, if an

argument has type `Foo`, you can declare it as either `Foo` or `const Foo&`,

whichever is appropriate.

A predicate-formatter returns a `::testing::AssertionResult` object to indicate

whether the assertion has succeeded or not. The only way to create such an

object is to call one of these factory functions:

As an example, let's improve the failure message in the previous example, which uses `EXPECT_PRED2()`:

```

// Returns the smallest prime common divisor of m and n,

// or 1 when m and n are mutually prime.

int SmallestPrimeCommonDivisor(int m, int n) { ... }

// A predicate-formatter for asserting that two integers are mutually prime.

::testing::AssertionResult AssertMutuallyPrime(const char* m_expr,

                                               const char* n_expr,

                                               int m,

                                               int n) {

  if (MutuallyPrime(m, n))

    return ::testing::AssertionSuccess();

  return ::testing::AssertionFailure()

      << m_expr << " and " << n_expr << " (" << m << " and " << n

      << ") are not mutually prime, " << "as they have a common divisor "

      << SmallestPrimeCommonDivisor(m, n);

}

```

With this predicate-formatter, we can use

```

EXPECT_PRED_FORMAT2(AssertMutuallyPrime, b, c);

```

to generate the message

b and c (4 and 10) are not mutually prime, as they have a common divisor 2.

As you may have realized, many of the assertions we introduced earlier are

special cases of `(EXPECT|ASSERT)_PRED_FORMAT*`. In fact, most of them are

indeed defined using `(EXPECT|ASSERT)_PRED_FORMAT*`.

_Availability_: Linux, Windows, Mac.

## Floating-Point Comparison ##

Comparing floating-point numbers is tricky. Due to round-off errors, it is

very unlikely that two floating-points will match exactly. Therefore,

`ASSERT_EQ` 's naive comparison usually doesn't work. And since floating-points

can have a wide value range, no single fixed error bound works. It's better to

compare by a fixed relative error bound, except for values close to 0 due to

the loss of precision there.

In general, for floating-point comparison to make sense, the user needs to

carefully choose the error bound. If they don't want or care to, comparing in

terms of Units in the Last Place (ULPs) is a good default, and Google Test

provides assertions to do this. Full details about ULPs are quite long; if you

want to learn more, see

[this article on float comparison](http://www.cygnus-software.com/papers/comparingfloats/comparingfloats.htm).

### Floating-Point Macros ###

| **Fatal assertion** | **Nonfatal assertion** | **Verifies** |

|:--------------------|:-----------------------|:-------------|

| `ASSERT_FLOAT_EQ(`_val1, val2_`);`  | `EXPECT_FLOAT_EQ(`_val1, val2_`);` | the two `float` values are almost equal |

| `ASSERT_DOUBLE_EQ(`_val1, val2_`);` | `EXPECT_DOUBLE_EQ(`_val1, val2_`);` | the two `double` values are almost equal |

By "almost equal", we mean the two values are within 4 ULP's from each

other.

The following assertions allow you to choose the acceptable error bound:

| **Fatal assertion** | **Nonfatal assertion** | **Verifies** |

|:--------------------|:-----------------------|:-------------|

| `ASSERT_NEAR(`_val1, val2, abs\_error_`);` | `EXPECT_NEAR`_(val1, val2, abs\_error_`);` | the difference between _val1_ and _val2_ doesn't exceed the given absolute error |

_Availability_: Linux, Windows, Mac.

### Floating-Point Predicate-Format Functions ###

Some floating-point operations are useful, but not that often used. In order

to avoid an explosion of new macros, we provide them as predicate-format

functions that can be used in predicate assertion macros (e.g.

`EXPECT_PRED_FORMAT2`, etc).

```

EXPECT_PRED_FORMAT2(::testing::FloatLE, val1, val2);

EXPECT_PRED_FORMAT2(::testing::DoubleLE, val1, val2);

```

Verifies that _val1_ is less than, or almost equal to, _val2_. You can

replace `EXPECT_PRED_FORMAT2` in the above table with `ASSERT_PRED_FORMAT2`.

_Availability_: Linux, Windows, Mac.

## Windows HRESULT assertions ##

These assertions test for `HRESULT` success or failure.

| **Fatal assertion** | **Nonfatal assertion** | **Verifies** |

|:--------------------|:-----------------------|:-------------|

| `ASSERT_HRESULT_SUCCEEDED(`_expression_`);` | `EXPECT_HRESULT_SUCCEEDED(`_expression_`);` | _expression_ is a success `HRESULT` |

| `ASSERT_HRESULT_FAILED(`_expression_`);`    | `EXPECT_HRESULT_FAILED(`_expression_`);`    | _expression_ is a failure `HRESULT` |

The generated output contains the human-readable error message

associated with the `HRESULT` code returned by _expression_.

You might use them like this:

```

CComPtr shell;

ASSERT_HRESULT_SUCCEEDED(shell.CoCreateInstance(L"Shell.Application"));

CComVariant empty;

ASSERT_HRESULT_SUCCEEDED(shell->ShellExecute(CComBSTR(url), empty, empty, empty, empty));

```

_Availability_: Windows.

## 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 if the assertion is satisfied.  If the types are different,

the function call will fail to compile, and the compiler error message

will likely (depending on the compiler) show you the actual values of

`T1` and `T2`.  This is mainly useful inside template code.

_Caveat:_ When used inside a member function of a class template or a

function template, `StaticAssertTypeEq<T1, T2>()` is effective _only if_

the function is instantiated.  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

actually instantiated.  Instead, you need:

```

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

```

to cause a compiler error.

_Availability:_ Linux, Windows, Mac; since version 1.3.0.

## Assertion Placement ##

You can use assertions in any C++ function. In particular, it doesn't

have to be a method of the test fixture class. The one constraint is

that assertions that generate a fatal failure (`FAIL*` and `ASSERT_*`)

can only be used in void-returning functions. This is a consequence of

Google Test not using exceptions. By placing it in a non-void function

you'll get a confusing compile error like

`"error: void value not ignored as it ought to be"`.

If you need to use assertions in a function that returns non-void, one option

is to make the function return the value in an out parameter instead. For

example, you can rewrite `T2 Foo(T1 x)` to `void Foo(T1 x, T2* result)`. You

need to make sure that `*result` contains some sensible value even when the

function returns prematurely. As the function now returns `void`, you can use

any assertion inside of it.

If changing the function's type is not an option, you should just use

assertions that 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

fatal assertions in them. You'll get a compilation error if you try. A simple

workaround is to transfer the entire body of the constructor or destructor to a

private void-returning method. However, you should be aware that a fatal

assertion failure in a constructor does not terminate the current test, as your

intuition might suggest; it merely returns from the constructor early, possibly

leaving your object in a partially-constructed state. Likewise, a fatal

assertion failure in a destructor may leave your object in a

partially-destructed state. Use assertions carefully in these situations!

# Teaching Google Test How to Print Your Values #

When a test assertion such as `EXPECT_EQ` fails, Google Test prints the

argument values 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, STL

containers, and any type that supports the `<<` operator.  For other

types, it prints 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 it to do a better job at printing your particular type

than to dump the bytes.  To do that, define `<<` for your type:

```

#include <iostream>

namespace foo {

class Bar { ... };  // We want Google Test to be able to print instances of this.

// It's important that the << operator is defined in the SAME

// namespace that defines Bar.  C++'s look-up rules rely on that.

::std::ostream& operator<<(::std::ostream& os, const Bar& bar) {

  return os << bar.DebugString();  // whatever needed to print bar to os

}

}  // namespace foo

```

Sometimes, this might not be an option: your team may consider it bad

style to have a `<<` operator for `Bar`, or `Bar` may already have a

`<<` operator that doesn't do what you want (and you cannot change

it).  If so, you can instead define a `PrintTo()` function like this:

```

#include <iostream>

namespace foo {

class Bar { ... };

// It's important that PrintTo() is defined in the SAME

// namespace that defines Bar.  C++'s look-up rules rely on that.

void PrintTo(const Bar& bar, ::std::ostream* os) {

  *os << bar.DebugString();  // whatever needed to print bar to os

}

}  // namespace foo

```

If you have defined both `<<` and `PrintTo()`, the latter will be used

when Google Test is concerned.  This allows you to customize how the value

appears in Google Test's output without affecting code that relies on the

behavior of its `<<` operator.

If you want to print a value `x` using Google Test's value printer

yourself, just call `::testing::PrintToString(`_x_`)`, which

returns an `std::string`:

```

vector<pair<Bar, int> > bar_ints = GetBarIntVector();

EXPECT_TRUE(IsCorrectBarIntVector(bar_ints))

    << "bar_ints = " << ::testing::PrintToString(bar_ints);

```

# Death Tests #

In many applications, there are assertions that can cause application failure

if a condition is not met. These sanity checks, which ensure that the program

is in a known good state, are there to fail at the earliest possible time after

some program state is corrupted. If the assertion checks the wrong condition,

then the program may proceed in an erroneous state, which could lead to memory

corruption, security holes, or worse. Hence it is vitally important to test

that such assertion statements work as expected.

Since these precondition checks cause the processes to die, we call such tests

_death 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 the exception

and avoid the crash. If you want to verify exceptions thrown by your code,

see [Exception Assertions](#exception-assertions).

If you want to test `EXPECT_*()/ASSERT_*()` failures in your test code, see [Catching Failures](#catching-failures).

## How to Write a Death Test ##

Google Test has the following macros to support death tests:

| **Fatal assertion** | **Nonfatal assertion** | **Verifies** |

|:--------------------|:-----------------------|:-------------|

| `ASSERT_DEATH(`_statement, regex_`);` | `EXPECT_DEATH(`_statement, regex_`);` | _statement_ crashes with the given error |

| `ASSERT_DEATH_IF_SUPPORTED(`_statement, regex_`);` | `EXPECT_DEATH_IF_SUPPORTED(`_statement, regex_`);` | if death tests are supported, verifies that _statement_ crashes with the given error; otherwise verifies nothing |

| `ASSERT_EXIT(`_statement, predicate, regex_`);` | `EXPECT_EXIT(`_statement, predicate, regex_`);` |_statement_ exits with the given error and its exit code matches _predicate_ |

where _statement_ is a statement that is expected to cause the process to

die, _predicate_ is a function or function object that evaluates an integer

exit status, and _regex_ is a regular expression that the stderr output of

_statement_ is expected to match. Note that _statement_ can be _any valid

statement_ (including _compound statement_) and doesn't have to be an

expression.

As usual, the `ASSERT` variants abort the current test function, while the

`EXPECT` variants do not.

**Note:** We use the word "crash" here to mean that the process

terminates with a _non-zero_ exit status code.  There are two

possibilities: either the process has called `exit()` or `_exit()`

with a non-zero value, or it may be killed by a signal.

This means that if _statement_ terminates the process with a 0 exit

code, it is _not_ considered a crash by `EXPECT_DEATH`.  Use

`EXPECT_EXIT` instead if this is the case, or if you want to restrict

the exit code more precisely.

A predicate here must accept an `int` and return a `bool`. The death test

succeeds only if the predicate returns `true`. Google Test defines a few

predicates that handle the most common cases:

```

::testing::ExitedWithCode(exit_code)

```

This expression is `true` if the program exited normally with the given exit

code.

```

::testing::KilledBySignal(signal_number)  // Not available on Windows.

```

This expression is `true` if the program was killed by the given signal.

The `*_DEATH` macros are convenient wrappers for `*_EXIT` that use a predicate

that verifies the process' exit code is non-zero.

Note that a death test only cares about three things:

  1. does _statement_ abort or exit the process?

  1. (in the case of `ASSERT_EXIT` and `EXPECT_EXIT`) does the exit status satisfy _predicate_?  Or (in the case of `ASSERT_DEATH` and `EXPECT_DEATH`) is the exit status non-zero?  And

  1. does the stderr output match _regex_?

In particular, if _statement_ generates an `ASSERT_*` or `EXPECT_*` failure, it will **not** cause the death test to fail, as Google Test assertions don't abort the process.

To write a death test, simply use one of the above 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, KillMyself) {

  EXPECT_EXIT(KillMyself(), ::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 and exit with exit code 0, and

  * calling `KillMyself()` kills the process with signal `SIGKILL`.

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

necessary.

_Important:_ We strongly recommend you to follow the convention of naming your

test case (not test) `*DeathTest` when it contains a death test, as

demonstrated in the above example. The `Death Tests And Threads` section below

explains why.

If a test fixture class is shared by normal tests and death tests, you

can use typedef to introduce an alias for the fixture class and avoid

duplicating its code:

```

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

typedef FooTest FooDeathTest;

TEST_F(FooTest, DoesThis) {

  // normal test

}

TEST_F(FooDeathTest, DoesThat) {

  // death test

}

```

_Availability:_ Linux, Windows (requires MSVC 8.0 or above), Cygwin, and Mac (the latter three are supported since v1.3.0).  `(ASSERT|EXPECT)_DEATH_IF_SUPPORTED` are new in v1.4.0.

## Regular Expression Syntax ##

On POSIX systems (e.g. Linux, Cygwin, and Mac), Google Test uses the

[POSIX extended regular expression](http://www.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap09.html#tag_09_04)

syntax in death tests. To learn about this syntax, you may want to read this [Wikipedia entry](http://en.wikipedia.org/wiki/Regular_expression#POSIX_Extended_Regular_Expressions).

On Windows, Google Test uses its own simple regular expression

implementation. It lacks many features you can find in POSIX extended

regular expressions.  For example, we don't support union (`"x|y"`),

grouping (`"(xy)"`), brackets (`"[xy]"`), and repetition count

(`"x{5,7}"`), among others. Below is what we do support (Letter `A` denotes a

literal character, period (`.`), or a single `\\` escape sequence; `x`

and `y` denote regular expressions.):

| `c` | matches any literal character `c` |

|:----|:----------------------------------|

| `\\d` | matches any decimal digit         |

| `\\D` | matches any character that's not a decimal digit |

| `\\f` | matches `\f`                      |

| `\\n` | matches `\n`                      |

| `\\r` | matches `\r`                      |

| `\\s` | matches any ASCII whitespace, including `\n` |

| `\\S` | matches any character that's not a whitespace |

| `\\t` | matches `\t`                      |

| `\\v` | matches `\v`                      |

| `\\w` | matches any letter, `_`, or decimal digit |

| `\\W` | matches any character that `\\w` doesn't match |

| `\\c` | matches any literal character `c`, which must be a punctuation |

| `\\.` | matches the `.` character         |

| `.` | matches any single character except `\n` |

| `A?` | matches 0 or 1 occurrences of `A` |

| `A*` | matches 0 or many occurrences of `A` |

| `A+` | matches 1 or many occurrences of `A` |

| `^` | matches the beginning of a string (not that of each line) |

| `$` | matches the end of a string (not that of each line) |

| `xy` | matches `x` followed by `y`       |

To help you determine which capability is available on your system,

Google Test defines macro `GTEST_USES_POSIX_RE=1` when it uses POSIX

extended regular expressions, or `GTEST_USES_SIMPLE_RE=1` when it uses

the simple version.  If you want your death tests to work in both

cases, you can either `#if` on these macros or use the more limited

syntax only.

## How It Works ##

Under the hood, `ASSERT_EXIT()` spawns a new process and executes the

death test statement in that process. The details of of how precisely

that happens depend on the platform and the variable

`::testing::GTEST_FLAG(death_test_style)` (which is initialized from the

command-line flag `--gtest_death_test_style`).

  * On POSIX systems, `fork()` (or `clone()` on Linux) is used to spawn the child, after which:

    * If the variable's value is `"fast"`, the death test statement is immediately executed.

    * If the variable's value is `"threadsafe"`, the child process re-executes the unit test binary just as it was originally invoked, but with some extra flags to cause just the single death test under consideration to be run.

  * On Windows, the child is spawned using the `CreateProcess()` API, and re-executes the binary to cause just the single death test under consideration to be run - much like the `threadsafe` mode on POSIX.

Other values for the variable are illegal and will cause the death test to

fail. Currently, the flag's default value is `"fast"`. However, we reserve the

right to change it in the future. Therefore, your tests should not depend on

this.

In either case, the parent process waits for the child process to complete, and checks that

  1. the child's exit status satisfies the predicate, and

  1. the child's stderr matches the regular expression.

If the death test statement runs to completion without dying, the child

process will nonetheless terminate, and the assertion fails.

## Death Tests And Threads ##

The reason for the two death test styles has to do with thread safety. Due to

well-known problems with forking in the presence of threads, death tests should

be run in a single-threaded context. Sometimes, however, it isn't feasible to

arrange that kind of environment. For example, statically-initialized modules

may start threads before main is ever reached. Once threads have been created,

it may be difficult or impossible to clean them up.

Google Test has three features intended to raise awareness of threading issues.

  1. A warning is emitted if multiple threads are running when a death test is encountered.

  1. Test cases with a name ending in "DeathTest" are run before all other tests.

  1. 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 likely to 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 are

executed in a separate process and cannot affect the parent.

## Death Test Styles ##

The "threadsafe" death test style was introduced in order to help mitigate the

risks of testing in a possibly multithreaded environment. It trades increased

test execution time (potentially dramatically so) for improved thread safety.

We suggest using the faster, default "fast" style unless your test has specific

problems with it.

You can choose a particular style of death tests by setting the flag

programmatically:

```

::testing::FLAGS_gtest_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 and restored afterwards, so you need not do that yourself. For example:

```

TEST(MyDeathTest, TestOne) {

  ::testing::FLAGS_gtest_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(), "");

}

int main(int argc, char** argv) {

  ::testing::InitGoogleTest(&argc, argv);

  ::testing::FLAGS_gtest_death_test_style = "fast";

  return RUN_ALL_TESTS();

}

```

## Caveats ##

The _statement_ argument of `ASSERT_EXIT()` can be any valid C++ statement.

If it leaves the current function via a `return` statement or by throwing an exception,

the death test is considered to have failed.  Some Google Test macros may return

from the current function (e.g. `ASSERT_TRUE()`), so be sure to avoid them 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 observable

in 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 the

memory reclaimed. To solve this problem, you can

  1. try not to free memory in a death test;

  1. free the memory again in the parent process; or

  1. do not use the heap checker in your program.

Due to an implementation detail, you cannot place multiple death test

assertions on the same line; otherwise, compilation will fail with an unobvious

error message.

Despite the improved thread safety afforded by the "threadsafe" style of death

test, thread problems such as deadlock are still possible in the presence of

handlers registered with `pthread_atfork(3)`.

# Using Assertions in Sub-routines #

## Adding Traces to Assertions ##

If a test sub-routine is called from several places, when an assertion

inside it fails, it can be hard to tell which invocation of the

sub-routine the failure is from.  You can alleviate this problem using

extra logging or custom failure messages, but that usually clutters up

your tests. A better solution is to use the `SCOPED_TRACE` macro:

| `SCOPED_TRACE(`_message_`);` |

|:-----------------------------|

where _message_ can be anything streamable to `std::ostream`. This

macro will cause the current file name, line number, and the given

message to be added in every failure message. The effect will be

undone when the control leaves the current lexical scope.

For example,

```

10: void Sub1(int n) {

11:   EXPECT_EQ(1, Bar(n));

12:   EXPECT_EQ(2, Bar(n + 1));

13: }

14:

15: TEST(FooTest, Bar) {

16:   {

17:     SCOPED_TRACE("A");  // This trace point will be included in

18:                         // 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: Failure

Value of: Bar(n)

Expected: 1

  Actual: 2

   Trace:

path/to/foo_test.cc:17: A

path/to/foo_test.cc:12: Failure

Value of: Bar(n + 1)

Expected: 2

  Actual: 3

```

Without the trace, it would've been difficult to know which invocation

of `Sub1()` the two failures come from respectively. (You could add an

extra message to each assertion in `Sub1()` to indicate the value of

`n`, but that's tedious.)

Some tips on using `SCOPED_TRACE`:

  1. With a suitable message, it's often enough to use `SCOPED_TRACE` at the beginning of a sub-routine, instead of at each call site.

  1. When calling sub-routines inside a loop, make the loop iterator part of the message in `SCOPED_TRACE` such that you can know which iteration the failure is from.

  1. Sometimes the line number of the trace point is enough for identifying the particular invocation of a sub-routine. In this case, you don't have to choose a unique message for `SCOPED_TRACE`. You can simply use `""`.

  1. You can use `SCOPED_TRACE` in an inner scope when there is one in the outer scope. In this case, all active trace points will be included in the failure messages, in reverse order they are encountered.

  1. The trace dump is clickable in Emacs' compilation buffer - hit return on a line number and you'll be taken to that line in the source file!

_Availability:_ Linux, Windows, Mac.

## Propagating Fatal Failures ##

A common pitfall when using `ASSERT_*` and `FAIL*` is not understanding that

when they fail they only abort the _current function_, not the entire test. For

example, 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 = NULL;

  *p = 3; // Segfault!

}

```

Since we don't use exceptions, it is technically impossible to

implement the intended behavior here.  To alleviate this, Google Test

provides two solutions.  You could use either the

`(ASSERT|EXPECT)_NO_FATAL_FAILURE` assertions or the

`HasFatalFailure()` function.  They are described in the following two

subsections.