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`.

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.
`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:
```
using ::std::get;
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`.

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

Matcher	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:

The MATCHER* macros cannot be used inside a function or class.
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).
You can use PrintToString(x) to convert a value x of any type to a string.

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);
}