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# 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`) aredivided 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 ordestructed later. If the compiler complains that `value` doesn't have a publiccopy 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 matcherwill be changed.
`IsTrue` and `IsFalse` are useful when you need to use a matcher, or for typesthat can be explicitly converted to Boolean, but are not implicitly converted toBoolean. In other cases, you can use the basic[`EXPECT_TRUE` and `EXPECT_FALSE`](assertions.md#boolean) assertions.
## Floating-Point Matchers {#FpMatchers}
| 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 ofthe 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 auser 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. Theyuse the regular expression syntax defined[here](../advanced.md#regular-expression-syntax). 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 towrite the elements in-line, match them more flexibly, or get more informativemessages, 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](#MultiArgMatchers)).* 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:
```cpp 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:
```cpp 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 {#MultiArgMatchers}
Technically, all matchers match a *single* value. A "multi-argument" matcher isjust one that matches a *tuple*. The following matchers can be used to match atuple `(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 (orreorder 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](../gmock_cook_book.md#SafeMatcherCast) 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 {#MatchersAsPredicatesCheat}
| 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:**
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:
```cpp MATCHER_P(NestedPropertyMatches, matcher, "") { return ExplainMatchResult(matcher, arg.nested().property(), result_listener); } ```
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