googletest/docs/reference/assertions.md

Assertions Reference

This page lists the assertion macros provided by GoogleTest for verifying code behavior. To use them, add #include <gtest/gtest.h>.

The majority of the macros listed below come as a pair with an EXPECT_ variant and an ASSERT_ variant. Upon failure, EXPECT_ macros generate nonfatal failures and allow the current function to continue running, while ASSERT_ macros generate fatal failures and abort the current function.

All assertion macros support streaming a custom failure message into them with the << operator, for example:

EXPECT_TRUE(my_condition) << "My condition is not true";

Anything that can be streamed to an ostream can be streamed to an assertion macro—in particular, C strings and string objects. If a wide string (wchar_t*, TCHAR* in UNICODE mode on Windows, or std::wstring) is streamed to an assertion, it will be translated to UTF-8 when printed.

Explicit Success and Failure

The assertions in this section generate a success or failure directly instead of testing a value or expression. These are useful when control flow, rather than a Boolean expression, determines the test's success or failure, as shown by the following example:

switch(expression) {
  case 1:
    ... some checks ...
  case 2:
    ... some other checks ...
  default:
    FAIL() << "We shouldn't get here.";
}

SUCCEED

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.

The SUCCEED assertion is purely documentary and currently doesn't generate any user-visible output. However, we may add SUCCEED messages to GoogleTest output in the future.

FAIL

FAIL()

Generates a fatal failure, which returns from the current function.

Can only be used in functions that return void. See Assertion Placement for more information.

ADD_FAILURE

ADD_FAILURE()

Generates a nonfatal failure, which allows the current function to continue running.

ADD_FAILURE_AT

ADD_FAILURE_AT(file_path,line_number)

Generates a nonfatal failure at the file and line number specified.

Generalized Assertion

The following assertion allows matchers to be used to verify values.

EXPECT_THAT

EXPECT_THAT(value,matcher)
ASSERT_THAT(value,matcher)

Verifies that value matches the matcher matcher.

For example, the following code verifies that the string value1 starts with "Hello", value2 matches a regular expression, and value3 is between 5 and 10:

#include <gmock/gmock.h>

using ::testing::AllOf;
using ::testing::Gt;
using ::testing::Lt;
using ::testing::MatchesRegex;
using ::testing::StartsWith;

...
EXPECT_THAT(value1, StartsWith("Hello"));
EXPECT_THAT(value2, MatchesRegex("Line \\d+"));
ASSERT_THAT(value3, AllOf(Gt(5), Lt(10)));

Matchers enable assertions of this form to read like English and generate informative failure messages. For example, if the above assertion on value1 fails, the resulting message will be similar to the following:

Value of: value1
  Actual: "Hi, world!"
Expected: starts with "Hello"

GoogleTest provides a built-in library of matchers—see the Matchers Reference. It is also possible to write your own matchers—see Writing New Matchers Quickly. The use of matchers makes EXPECT_THAT a powerful, extensible assertion.

The idea for this assertion was borrowed from Joe Walnes' Hamcrest project, which adds assertThat() to JUnit.

Boolean Conditions

The following assertions test Boolean conditions.

EXPECT_TRUE

EXPECT_TRUE(condition)
ASSERT_TRUE(condition)

Verifies that condition is true.

EXPECT_FALSE

EXPECT_FALSE(condition)
ASSERT_FALSE(condition)

Verifies that condition is false.

Binary Comparison

The following assertions compare two values. The value arguments must be comparable by the assertion's comparison operator, otherwise a compiler error will result.

If an argument supports the << operator, it will be called to print the argument when the assertion fails. Otherwise, GoogleTest will attempt to print them in the best way it can—see Teaching GoogleTest How to Print Your Values.

Arguments are always evaluated exactly once, so it's OK for the arguments to have side effects. However, the argument evaluation order is undefined and programs should not depend on any particular argument evaluation order.

These assertions work with both narrow and wide string objects (string and wstring).

See also the Floating-Point Comparison assertions to compare floating-point numbers and avoid problems caused by rounding.

EXPECT_EQ

EXPECT_EQ(val1,val2)
ASSERT_EQ(val1,val2)

Verifies that val1==val2.

Does pointer equality on pointers. If used on two C strings, it tests if they are in the same memory location, not if they have the same value. Use EXPECT_STREQ to compare C strings (e.g. const char*) by value.

When comparing a pointer to NULL, use EXPECT_EQ(ptr, nullptr) instead of EXPECT_EQ(ptr, NULL).

EXPECT_NE

EXPECT_NE(val1,val2)
ASSERT_NE(val1,val2)

Verifies that val1!=val2.

Does pointer equality on pointers. If used on two C strings, it tests if they are in different memory locations, not if they have different values. Use EXPECT_STRNE to compare C strings (e.g. const char*) by value.

When comparing a pointer to NULL, use EXPECT_NE(ptr, nullptr) instead of EXPECT_NE(ptr, NULL).

EXPECT_LT

EXPECT_LT(val1,val2)
ASSERT_LT(val1,val2)

Verifies that val1<val2.

EXPECT_LE

EXPECT_LE(val1,val2)
ASSERT_LE(val1,val2)

Verifies that val1<=val2.

EXPECT_GT

EXPECT_GT(val1,val2)
ASSERT_GT(val1,val2)

Verifies that val1>val2.

EXPECT_GE

EXPECT_GE(val1,val2)
ASSERT_GE(val1,val2)

Verifies that val1>=val2.

String Comparison

The following assertions compare two C strings. To compare two string objects, use EXPECT_EQ or EXPECT_NE instead.

These assertions also accept wide C strings (wchar_t*). If a comparison of two wide strings fails, their values will be printed as UTF-8 narrow strings.

To compare a C string with NULL, use EXPECT_EQ(c_string, nullptr) or EXPECT_NE(c_string, nullptr).

EXPECT_STREQ

EXPECT_STREQ(str1,str2)
ASSERT_STREQ(str1,str2)

Verifies that the two C strings str1 and str2 have the same contents.

EXPECT_STRNE

EXPECT_STRNE(str1,str2)
ASSERT_STRNE(str1,str2)

Verifies that the two C strings str1 and str2 have different contents.

EXPECT_STRCASEEQ

EXPECT_STRCASEEQ(str1,str2)
ASSERT_STRCASEEQ(str1,str2)

Verifies that the two C strings str1 and str2 have the same contents, ignoring case.

EXPECT_STRCASENE

EXPECT_STRCASENE(str1,str2)
ASSERT_STRCASENE(str1,str2)

Verifies that the two C strings str1 and str2 have different contents, ignoring case.

Floating-Point Comparison

The following assertions compare two floating-point values.

Due to rounding errors, it is very unlikely that two floating-point values will match exactly, so EXPECT_EQ is not suitable. In general, for floating-point comparison to make sense, the user needs to carefully choose the error bound.

GoogleTest also provides assertions that use a default error bound based on Units in the Last Place (ULPs). To learn more about ULPs, see the article Comparing Floating Point Numbers.

EXPECT_FLOAT_EQ

EXPECT_FLOAT_EQ(val1,val2)
ASSERT_FLOAT_EQ(val1,val2)

Verifies that the two float values val1 and val2 are approximately equal, to within 4 ULPs from each other. Infinity and the largest finite float value are considered to be one ULP apart.

EXPECT_DOUBLE_EQ

EXPECT_DOUBLE_EQ(val1,val2)
ASSERT_DOUBLE_EQ(val1,val2)

Verifies that the two double values val1 and val2 are approximately equal, to within 4 ULPs from each other. Infinity and the largest finite double value are considered to be one ULP apart.

EXPECT_NEAR

EXPECT_NEAR(val1,val2,abs_error)
ASSERT_NEAR(val1,val2,abs_error)

Verifies that the difference between val1 and val2 does not exceed the absolute error bound abs_error.

If val and val2 are both infinity of the same sign, the difference is considered to be 0. Otherwise, if either value is infinity, the difference is considered to be infinity. All non-NaN values (including infinity) are considered to not exceed an abs_error of infinity.

Exception Assertions

The following assertions verify that a piece of code throws, or does not throw, an exception. Usage requires exceptions to be enabled in the build environment.

Note that the piece of code under test can be a compound statement, for example:

EXPECT_NO_THROW({
  int n = 5;
  DoSomething(&n);
});

EXPECT_THROW

EXPECT_THROW(statement,exception_type)
ASSERT_THROW(statement,exception_type)

Verifies that statement throws an exception of type exception_type.

EXPECT_ANY_THROW

EXPECT_ANY_THROW(statement)
ASSERT_ANY_THROW(statement)

Verifies that statement throws an exception of any type.

EXPECT_NO_THROW

EXPECT_NO_THROW(statement)
ASSERT_NO_THROW(statement)

Verifies that statement does not throw any exception.

Predicate Assertions

The following assertions enable more complex predicates to be verified while printing a more clear failure message than if EXPECT_TRUE were used alone.

EXPECT_PRED*

EXPECT_PRED1(pred,val1)
EXPECT_PRED2(pred,val1,val2)
EXPECT_PRED3(pred,val1,val2,val3)
EXPECT_PRED4(pred,val1,val2,val3,val4)
EXPECT_PRED5(pred,val1,val2,val3,val4,val5)

ASSERT_PRED1(pred,val1)
ASSERT_PRED2(pred,val1,val2)
ASSERT_PRED3(pred,val1,val2,val3)
ASSERT_PRED4(pred,val1,val2,val3,val4)
ASSERT_PRED5(pred,val1,val2,val3,val4,val5)

Verifies that the predicate pred returns true when passed the given values as arguments.

The parameter pred is a function or functor that accepts as many arguments as the corresponding macro accepts values. If pred returns true for the given arguments, the assertion succeeds, otherwise the assertion fails.

When the assertion fails, it prints the value of each argument. Arguments are always evaluated exactly once.

As an example, see the following code:

// Returns true if 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;
...
EXPECT_PRED2(MutuallyPrime, a, b);  // Succeeds
EXPECT_PRED2(MutuallyPrime, b, c);  // Fails

In the above example, the first assertion succeeds, and the second fails with the following message:

MutuallyPrime(b, c) is false, where
b is 4
c is 10

Note that if the given predicate is an overloaded function or a function template, the assertion macro might not be able to determine which version to use, and it might be necessary to explicitly specify the type of the function. For example, for a Boolean function IsPositive() overloaded to take either a single int or double argument, it would be necessary to write one of the following:

EXPECT_PRED1(static_cast<bool (*)(int)>(IsPositive), 5);
EXPECT_PRED1(static_cast<bool (*)(double)>(IsPositive), 3.14);

Writing simply EXPECT_PRED1(IsPositive, 5); would result in a compiler error. Similarly, to use a template function, specify the template arguments:

template <typename T>
bool IsNegative(T x) {
  return x < 0;
}
...
EXPECT_PRED1(IsNegative<int>, -5);  // Must specify type for IsNegative

If a template has multiple parameters, wrap the predicate in parentheses so the macro arguments are parsed correctly:

ASSERT_PRED2((MyPredicate<int, int>), 5, 0);

EXPECT_PRED_FORMAT*

EXPECT_PRED_FORMAT1(pred_formatter,val1)
EXPECT_PRED_FORMAT2(pred_formatter,val1,val2)
EXPECT_PRED_FORMAT3(pred_formatter,val1,val2,val3)
EXPECT_PRED_FORMAT4(pred_formatter,val1,val2,val3,val4)
EXPECT_PRED_FORMAT5(pred_formatter,val1,val2,val3,val4,val5)

ASSERT_PRED_FORMAT1(pred_formatter,val1)
ASSERT_PRED_FORMAT2(pred_formatter,val1,val2)
ASSERT_PRED_FORMAT3(pred_formatter,val1,val2,val3)
ASSERT_PRED_FORMAT4(pred_formatter,val1,val2,val3,val4)
ASSERT_PRED_FORMAT5(pred_formatter,val1,val2,val3,val4,val5)

Verifies that the predicate pred_formatter succeeds when passed the given values as arguments.

The parameter pred_formatter is a predicate-formatter, which is a function or functor with the signature:

testing::AssertionResult PredicateFormatter(const char* expr1,
                                            const char* expr2,
                                            ...
                                            const char* exprn,
                                            T1 val1,
                                            T2 val2,
                                            ...
                                            Tn valn);

where val1, val2, ..., valn are the values of the predicate arguments, and expr1, expr2, ..., exprn are the corresponding expressions as they appear in the source code. The types T1, T2, ..., Tn can be either value types or reference types; if an argument has type T, it can be declared as either T or const T&, whichever is appropriate. For more about the return type testing::AssertionResult, see Using a Function That Returns an AssertionResult.

As an example, see the following code:

// 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) { ... }

// Returns true if m and n have no common divisors except 1.
bool MutuallyPrime(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);
}

...
const int a = 3;
const int b = 4;
const int c = 10;
...
EXPECT_PRED_FORMAT2(AssertMutuallyPrime, a, b);  // Succeeds
EXPECT_PRED_FORMAT2(AssertMutuallyPrime, b, c);  // Fails

In the above example, the final assertion fails and the predicate-formatter produces the following failure message:

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

Windows HRESULT Assertions

The following assertions test for HRESULT success or failure. For example:

CComPtr<IShellDispatch2> shell;
ASSERT_HRESULT_SUCCEEDED(shell.CoCreateInstance(L"Shell.Application"));
CComVariant empty;
ASSERT_HRESULT_SUCCEEDED(shell->ShellExecute(CComBSTR(url), empty, empty, empty, empty));

The generated output contains the human-readable error message associated with the returned HRESULT code.

EXPECT_HRESULT_SUCCEEDED

EXPECT_HRESULT_SUCCEEDED(expression)
ASSERT_HRESULT_SUCCEEDED(expression)

Verifies that expression is a success HRESULT.

EXPECT_HRESULT_FAILED

EXPECT_HRESULT_FAILED(expression)
ASSERT_HRESULT_FAILED(expression)

Verifies that expression is a failure HRESULT.

Death Assertions

The following assertions verify that a piece of code causes the process to terminate. For context, see Death Tests.

These assertions spawn a new process and execute the code under test in that process. How that happens depends 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".

If the death test statement runs to completion without dying, the child process will nonetheless terminate, and the assertion fails.

Note that the piece of code under test can be a compound statement, for example:

EXPECT_DEATH({
  int n = 5;
  DoSomething(&n);
}, "Error on line .* of DoSomething()");

EXPECT_DEATH

EXPECT_DEATH(statement,matcher)
ASSERT_DEATH(statement,matcher)

Verifies that statement causes the process to terminate with a nonzero exit status and produces stderr output that matches matcher.

The parameter matcher is either a matcher for a const std::string&, or a regular expression (see Regular Expression Syntax)—a bare string s (with no matcher) is treated as ContainsRegex(s), not Eq(s).

For example, the following code verifies that calling DoSomething(42) causes the process to die with an error message that contains the text My error:

EXPECT_DEATH(DoSomething(42), "My error");

EXPECT_DEATH_IF_SUPPORTED

EXPECT_DEATH_IF_SUPPORTED(statement,matcher)
ASSERT_DEATH_IF_SUPPORTED(statement,matcher)

If death tests are supported, behaves the same as EXPECT_DEATH. Otherwise, verifies nothing.

EXPECT_DEBUG_DEATH

EXPECT_DEBUG_DEATH(statement,matcher)
ASSERT_DEBUG_DEATH(statement,matcher)

In debug mode, behaves the same as EXPECT_DEATH. When not in debug mode (i.e. NDEBUG is defined), just executes statement.

EXPECT_EXIT

EXPECT_EXIT(statement,predicate,matcher)
ASSERT_EXIT(statement,predicate,matcher)

Verifies that statement causes the process to terminate with an exit status that satisfies predicate, and produces stderr output that matches matcher.

The parameter predicate is a function or functor that accepts an int exit status and returns a bool. GoogleTest provides two predicates to handle common cases:

// Returns true if the program exited normally with the given exit status code.
::testing::ExitedWithCode(exit_code);

// Returns true if the program was killed by the given signal.
// Not available on Windows.
::testing::KilledBySignal(signal_number);

The parameter matcher is either a matcher for a const std::string&, or a regular expression (see Regular Expression Syntax)—a bare string s (with no matcher) is treated as ContainsRegex(s), not Eq(s).

For example, the following code verifies that calling NormalExit() causes the process to print a message containing the text Success to stderr and exit with exit status code 0:

EXPECT_EXIT(NormalExit(), testing::ExitedWithCode(0), "Success");