googletest/docs/reference/matchers.md

Matchers Reference

A matcher matches a single argument. You can use it inside ON_CALL() or EXPECT_CALL(), or use it to validate a value directly using two macros:

Macro	Description
EXPECT_THAT(actual_value, matcher)	Asserts that actual_value matches matcher.
ASSERT_THAT(actual_value, matcher)	The same as EXPECT_THAT(actual_value, matcher), except that it generates a fatal failure.

{: .callout .note} Note: Although equality matching via EXPECT_THAT(actual_value, expected_value) is supported, prefer to make the comparison explicit via EXPECT_THAT(actual_value, Eq(expected_value)) or EXPECT_EQ(actual_value, expected_value).

Built-in matchers (where argument is the function argument, e.g. actual_value in the example above, or when used in the context of EXPECT_CALL(mock_object, method(matchers)), the arguments of method) are divided into several categories. All matchers are defined in the ::testing namespace unless otherwise noted.

Wildcard

Matcher	Description
_	argument can be any value of the correct type.
A<type>() or An<type>()	argument can be any value of type type.

Generic Comparison

Matcher	Description
Eq(value) or value	argument == value
Ge(value)	argument >= value
Gt(value)	argument > value
Le(value)	argument <= value
Lt(value)	argument < value
Ne(value)	argument != value
IsFalse()	argument evaluates to false in a Boolean context.
IsTrue()	argument evaluates to true in a Boolean context.
IsNull()	argument is a NULL pointer (raw or smart).
NotNull()	argument is a non-null pointer (raw or smart).
Optional(m)	argument is optional<> that contains a value matching m. (For testing whether an optional<> is set, check for equality with nullopt. You may need to use Eq(nullopt) if the inner type doesn't have ==.)
VariantWith<T>(m)	argument is variant<> that holds the alternative of type T with a value matching m.
Ref(variable)	argument is a reference to variable.
TypedEq<type>(value)	argument has type type and is equal to value. You may need to use this instead of Eq(value) when the mock function is overloaded.

Except Ref(), these matchers make a copy of value in case it's modified or destructed later. If the compiler complains that value doesn't have a public copy constructor, try wrap it in std::ref(), e.g. Eq(std::ref(non_copyable_value)). If you do that, make sure non_copyable_value is not changed afterwards, or the meaning of your matcher will be changed.

IsTrue and IsFalse are useful when you need to use a matcher, or for types that can be explicitly converted to Boolean, but are not implicitly converted to Boolean. In other cases, you can use the basic EXPECT_TRUE and EXPECT_FALSE assertions.

Floating-Point Matchers

Matcher	Description
DoubleEq(a_double)	argument is a double value approximately equal to a_double, treating two NaNs as unequal.
FloatEq(a_float)	argument is a float value approximately equal to a_float, treating two NaNs as unequal.
NanSensitiveDoubleEq(a_double)	argument is a double value approximately equal to a_double, treating two NaNs as equal.
NanSensitiveFloatEq(a_float)	argument is a float value approximately equal to a_float, treating two NaNs as equal.
IsNan()	argument is any floating-point type with a NaN value.

The above matchers use ULP-based comparison (the same as used in googletest). They automatically pick a reasonable error bound based on the absolute value of the expected value. DoubleEq() and FloatEq() conform to the IEEE standard, which requires comparing two NaNs for equality to return false. The NanSensitive* version instead treats two NaNs as equal, which is often what a user wants.

Matcher	Description
DoubleNear(a_double, max_abs_error)	argument is a double value close to a_double (absolute error <= max_abs_error), treating two NaNs as unequal.
FloatNear(a_float, max_abs_error)	argument is a float value close to a_float (absolute error <= max_abs_error), treating two NaNs as unequal.
NanSensitiveDoubleNear(a_double, max_abs_error)	argument is a double value close to a_double (absolute error <= max_abs_error), treating two NaNs as equal.
NanSensitiveFloatNear(a_float, max_abs_error)	argument is a float value close to a_float (absolute error <= max_abs_error), treating two NaNs as equal.

String Matchers

The argument can be either a C string or a C++ string object:

Matcher	Description
ContainsRegex(string)	argument matches the given regular expression.
EndsWith(suffix)	argument ends with string suffix.
HasSubstr(string)	argument contains string as a sub-string.
IsEmpty()	argument is an empty string.
MatchesRegex(string)	argument matches the given regular expression with the match starting at the first character and ending at the last character.
StartsWith(prefix)	argument starts with string prefix.
StrCaseEq(string)	argument is equal to string, ignoring case.
StrCaseNe(string)	argument is not equal to string, ignoring case.
StrEq(string)	argument is equal to string.
StrNe(string)	argument is not equal to string.
WhenBase64Unescaped(m)	argument is a base-64 escaped string whose unescaped string matches m.

ContainsRegex() and MatchesRegex() take ownership of the RE object. They use the regular expression syntax defined here. All of these matchers, except ContainsRegex() and MatchesRegex() work for wide strings as well.

Container Matchers

Most STL-style containers support ==, so you can use Eq(expected_container) or simply expected_container to match a container exactly. If you want to write the elements in-line, match them more flexibly, or get more informative messages, you can use:

Matcher	Description
BeginEndDistanceIs(m)	argument is a container whose begin() and end() iterators are separated by a number of increments matching m. E.g. BeginEndDistanceIs(2) or BeginEndDistanceIs(Lt(2)). For containers that define a size() method, SizeIs(m) may be more efficient.
ContainerEq(container)	The same as Eq(container) except that the failure message also includes which elements are in one container but not the other.
Contains(e)	argument contains an element that matches e, which can be either a value or a matcher.
Contains(e).Times(n)	argument contains elements that match e, which can be either a value or a matcher, and the number of matches is n, which can be either a value or a matcher. Unlike the plain Contains and Each this allows to check for arbitrary occurrences including testing for absence with Contains(e).Times(0).
Each(e)	argument is a container where every element matches e, which can be either a value or a matcher.
ElementsAre(e0, e1, ..., en)	argument has n + 1 elements, where the i-th element matches ei, which can be a value or a matcher.
ElementsAreArray({e0, e1, ..., en}), ElementsAreArray(a_container), ElementsAreArray(begin, end), ElementsAreArray(array), or ElementsAreArray(array, count)	The same as ElementsAre() except that the expected element values/matchers come from an initializer list, STL-style container, iterator range, or C-style array.
IsEmpty()	argument is an empty container (container.empty()).
IsSubsetOf({e0, e1, ..., en}), IsSubsetOf(a_container), IsSubsetOf(begin, end), IsSubsetOf(array), or IsSubsetOf(array, count)	argument matches UnorderedElementsAre(x0, x1, ..., xk) for some subset {x0, x1, ..., xk} of the expected matchers.
IsSupersetOf({e0, e1, ..., en}), IsSupersetOf(a_container), IsSupersetOf(begin, end), IsSupersetOf(array), or IsSupersetOf(array, count)	Some subset of argument matches UnorderedElementsAre(expected matchers).
Pointwise(m, container), Pointwise(m, {e0, e1, ..., en})	argument contains the same number of elements as in container, and for all i, (the i-th element in argument, the i-th element in container) match m, which is a matcher on 2-tuples. E.g. Pointwise(Le(), upper_bounds) verifies that each element in argument doesn't exceed the corresponding element in upper_bounds. See more detail below.
SizeIs(m)	argument is a container whose size matches m. E.g. SizeIs(2) or SizeIs(Lt(2)).
UnorderedElementsAre(e0, e1, ..., en)	argument has n + 1 elements, and under some permutation of the elements, each element matches an ei (for a different i), which can be a value or a matcher.
UnorderedElementsAreArray({e0, e1, ..., en}), UnorderedElementsAreArray(a_container), UnorderedElementsAreArray(begin, end), UnorderedElementsAreArray(array), or UnorderedElementsAreArray(array, count)	The same as UnorderedElementsAre() except that the expected element values/matchers come from an initializer list, STL-style container, iterator range, or C-style array.
UnorderedPointwise(m, container), UnorderedPointwise(m, {e0, e1, ..., en})	Like Pointwise(m, container), but ignores the order of elements.
WhenSorted(m)	When argument is sorted using the < operator, it matches container matcher m. E.g. WhenSorted(ElementsAre(1, 2, 3)) verifies that argument contains elements 1, 2, and 3, ignoring order.
WhenSortedBy(comparator, m)	The same as WhenSorted(m), except that the given comparator instead of < is used to sort argument. E.g. WhenSortedBy(std::greater(), ElementsAre(3, 2, 1)).

Notes:

• These matchers can also match:

  1. a native array passed by reference (e.g. in Foo(const int (&a)[5])), and
  2. an array passed as a pointer and a count (e.g. in Bar(const T* buffer, int len) -- see Multi-argument Matchers).

• The array being matched may be multi-dimensional (i.e. its elements can be arrays).

• m in Pointwise(m, ...) and UnorderedPointwise(m, ...) should be a matcher for ::std::tuple<T, U> where T and U are the element type of the actual container and the expected container, respectively. For example, to compare two Foo containers where Foo doesn't support operator==, one might write:

  MATCHER(FooEq, "") {
    return std::get<0>(arg).Equals(std::get<1>(arg));
  }
  ...
  EXPECT_THAT(actual_foos, Pointwise(FooEq(), expected_foos));
  

Member Matchers

Matcher	Description
Field(&class::field, m)	argument.field (or argument->field when argument is a plain pointer) matches matcher m, where argument is an object of type class.
Field(field_name, &class::field, m)	The same as the two-parameter version, but provides a better error message.
Key(e)	argument.first matches e, which can be either a value or a matcher. E.g. Contains(Key(Le(5))) can verify that a map contains a key <= 5.
Pair(m1, m2)	argument is an std::pair whose first field matches m1 and second field matches m2.
FieldsAre(m...)	argument is a compatible object where each field matches piecewise with the matchers m.... A compatible object is any that supports the std::tuple_size<Obj>+get<I>(obj) protocol. In C++17 and up this also supports types compatible with structured bindings, like aggregates.
Property(&class::property, m)	argument.property() (or argument->property() when argument is a plain pointer) matches matcher m, where argument is an object of type class. The method property() must take no argument and be declared as const.
Property(property_name, &class::property, m)	The same as the two-parameter version, but provides a better error message.

Notes:

• You can use FieldsAre() to match any type that supports structured bindings, such as std::tuple, std::pair, std::array, and aggregate types. For example:

  std::tuple<int, std::string> my_tuple{7, "hello world"};
  EXPECT_THAT(my_tuple, FieldsAre(Ge(0), HasSubstr("hello")));
  
  struct MyStruct {
    int value = 42;
    std::string greeting = "aloha";
  };
  MyStruct s;
  EXPECT_THAT(s, FieldsAre(42, "aloha"));
  

• Don't use Property() against member functions that you do not own, because taking addresses of functions is fragile and generally not part of the contract of the function.

Matching the Result of a Function, Functor, or Callback

Matcher	Description
ResultOf(f, m)	f(argument) matches matcher m, where f is a function or functor.

Pointer Matchers

Matcher	Description
Address(m)	the result of std::addressof(argument) matches m.
Pointee(m)	argument (either a smart pointer or a raw pointer) points to a value that matches matcher m.
Pointer(m)	argument (either a smart pointer or a raw pointer) contains a pointer that matches m. m will match against the raw pointer regardless of the type of argument.
WhenDynamicCastTo<T>(m)	when argument is passed through dynamic_cast<T>(), it matches matcher m.

Multi-argument Matchers

Technically, all matchers match a single value. A "multi-argument" matcher is just one that matches a tuple. The following matchers can be used to match a tuple (x, y):

Matcher	Description
Eq()	x == y
Ge()	x >= y
Gt()	x > y
Le()	x <= y
Lt()	x < y
Ne()	x != y

You can use the following selectors to pick a subset of the arguments (or reorder them) to participate in the matching:

Matcher	Description
AllArgs(m)	Equivalent to m. Useful as syntactic sugar in .With(AllArgs(m)).
Args<N1, N2, ..., Nk>(m)	The tuple of the k selected (using 0-based indices) arguments matches m, e.g. Args<1, 2>(Eq()).

Composite Matchers

You can make a matcher from one or more other matchers:

Matcher	Description
AllOf(m1, m2, ..., mn)	argument matches all of the matchers m1 to mn.
AllOfArray({m0, m1, ..., mn}), AllOfArray(a_container), AllOfArray(begin, end), AllOfArray(array), or AllOfArray(array, count)	The same as AllOf() except that the matchers come from an initializer list, STL-style container, iterator range, or C-style array.
AnyOf(m1, m2, ..., mn)	argument matches at least one of the matchers m1 to mn.
AnyOfArray({m0, m1, ..., mn}), AnyOfArray(a_container), AnyOfArray(begin, end), AnyOfArray(array), or AnyOfArray(array, count)	The same as AnyOf() except that the matchers come from an initializer list, STL-style container, iterator range, or C-style array.
Not(m)	argument doesn't match matcher m.
Conditional(cond, m1, m2)	Matches matcher m1 if cond evaluates to true, else matches m2.

Adapters for Matchers

Matcher	Description
MatcherCast<T>(m)	casts matcher m to type Matcher<T>.
SafeMatcherCast<T>(m)	safely casts matcher m to type Matcher<T>.
Truly(predicate)	predicate(argument) returns something considered by C++ to be true, where predicate is a function or functor.

AddressSatisfies(callback) and Truly(callback) take ownership of callback, which must be a permanent callback.

Using Matchers as Predicates

Matcher	Description
Matches(m)(value)	evaluates to true if value matches m. You can use Matches(m) alone as a unary functor.
ExplainMatchResult(m, value, result_listener)	evaluates to true if value matches m, explaining the result to result_listener.
Value(value, m)	evaluates to true if value matches m.

Defining Matchers

Macro	Description
MATCHER(IsEven, "") { return (arg % 2) == 0; }	Defines a matcher IsEven() to match an even number.
MATCHER_P(IsDivisibleBy, n, "") { *result_listener << "where the remainder is " << (arg % n); return (arg % n) == 0; }	Defines a matcher IsDivisibleBy(n) to match a number divisible by n.
MATCHER_P2(IsBetween, a, b, absl::StrCat(negation ? "isn't" : "is", " between ", PrintToString(a), " and ", PrintToString(b))) { return a <= arg && arg <= b; }	Defines a matcher IsBetween(a, b) to match a value in the range [a, b].

Notes:

1. The MATCHER* macros cannot be used inside a function or class.

2. The matcher body must be purely functional (i.e. it cannot have any side effect, and the result must not depend on anything other than the value being matched and the matcher parameters).

3. You can use PrintToString(x) to convert a value x of any type to a string.

4. You can use ExplainMatchResult() in a custom matcher to wrap another matcher, for example:

   MATCHER_P(NestedPropertyMatches, matcher, "") {
     return ExplainMatchResult(matcher, arg.nested().property(), result_listener);
   }