1# Matchers Reference 2 3A **matcher** matches a *single* argument. You can use it inside `ON_CALL()` or 4`EXPECT_CALL()`, or use it to validate a value directly using two macros: 5 6| Macro | Description | 7| :----------------------------------- | :------------------------------------ | 8| `EXPECT_THAT(actual_value, matcher)` | Asserts that `actual_value` matches `matcher`. | 9| `ASSERT_THAT(actual_value, matcher)` | The same as `EXPECT_THAT(actual_value, matcher)`, except that it generates a **fatal** failure. | 10 11{: .callout .note} 12**Note:** Although equality matching via `EXPECT_THAT(actual_value, 13expected_value)` is supported, prefer to make the comparison explicit via 14`EXPECT_THAT(actual_value, Eq(expected_value))` or `EXPECT_EQ(actual_value, 15expected_value)`. 16 17Built-in matchers (where `argument` is the function argument, e.g. 18`actual_value` in the example above, or when used in the context of 19`EXPECT_CALL(mock_object, method(matchers))`, the arguments of `method`) are 20divided into several categories. All matchers are defined in the `::testing` 21namespace unless otherwise noted. 22 23## Wildcard 24 25Matcher | Description 26:-------------------------- | :----------------------------------------------- 27`_` | `argument` can be any value of the correct type. 28`A<type>()` or `An<type>()` | `argument` can be any value of type `type`. 29 30## Generic Comparison 31 32| Matcher | Description | 33| :--------------------- | :-------------------------------------------------- | 34| `Eq(value)` or `value` | `argument == value` | 35| `Ge(value)` | `argument >= value` | 36| `Gt(value)` | `argument > value` | 37| `Le(value)` | `argument <= value` | 38| `Lt(value)` | `argument < value` | 39| `Ne(value)` | `argument != value` | 40| `IsFalse()` | `argument` evaluates to `false` in a Boolean context. | 41| `IsTrue()` | `argument` evaluates to `true` in a Boolean context. | 42| `IsNull()` | `argument` is a `NULL` pointer (raw or smart). | 43| `NotNull()` | `argument` is a non-null pointer (raw or smart). | 44| `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 `==`.)| 45| `VariantWith<T>(m)` | `argument` is `variant<>` that holds the alternative of type T with a value matching `m`. | 46| `Ref(variable)` | `argument` is a reference to `variable`. | 47| `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. | 48 49Except `Ref()`, these matchers make a *copy* of `value` in case it's modified or 50destructed later. If the compiler complains that `value` doesn't have a public 51copy constructor, try wrap it in `std::ref()`, e.g. 52`Eq(std::ref(non_copyable_value))`. If you do that, make sure 53`non_copyable_value` is not changed afterwards, or the meaning of your matcher 54will be changed. 55 56`IsTrue` and `IsFalse` are useful when you need to use a matcher, or for types 57that can be explicitly converted to Boolean, but are not implicitly converted to 58Boolean. In other cases, you can use the basic 59[`EXPECT_TRUE` and `EXPECT_FALSE`](assertions.md#boolean) assertions. 60 61## Floating-Point Matchers {#FpMatchers} 62 63| Matcher | Description | 64| :------------------------------- | :--------------------------------- | 65| `DoubleEq(a_double)` | `argument` is a `double` value approximately equal to `a_double`, treating two NaNs as unequal. | 66| `FloatEq(a_float)` | `argument` is a `float` value approximately equal to `a_float`, treating two NaNs as unequal. | 67| `NanSensitiveDoubleEq(a_double)` | `argument` is a `double` value approximately equal to `a_double`, treating two NaNs as equal. | 68| `NanSensitiveFloatEq(a_float)` | `argument` is a `float` value approximately equal to `a_float`, treating two NaNs as equal. | 69| `IsNan()` | `argument` is any floating-point type with a NaN value. | 70 71The above matchers use ULP-based comparison (the same as used in googletest). 72They automatically pick a reasonable error bound based on the absolute value of 73the expected value. `DoubleEq()` and `FloatEq()` conform to the IEEE standard, 74which requires comparing two NaNs for equality to return false. The 75`NanSensitive*` version instead treats two NaNs as equal, which is often what a 76user wants. 77 78| Matcher | Description | 79| :------------------------------------------------ | :----------------------- | 80| `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. | 81| `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. | 82| `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. | 83| `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. | 84 85## String Matchers 86 87The `argument` can be either a C string or a C++ string object: 88 89| Matcher | Description | 90| :---------------------- | :------------------------------------------------- | 91| `ContainsRegex(string)` | `argument` matches the given regular expression. | 92| `EndsWith(suffix)` | `argument` ends with string `suffix`. | 93| `HasSubstr(string)` | `argument` contains `string` as a sub-string. | 94| `IsEmpty()` | `argument` is an empty string. | 95| `MatchesRegex(string)` | `argument` matches the given regular expression with the match starting at the first character and ending at the last character. | 96| `StartsWith(prefix)` | `argument` starts with string `prefix`. | 97| `StrCaseEq(string)` | `argument` is equal to `string`, ignoring case. | 98| `StrCaseNe(string)` | `argument` is not equal to `string`, ignoring case. | 99| `StrEq(string)` | `argument` is equal to `string`. | 100| `StrNe(string)` | `argument` is not equal to `string`. | 101 102`ContainsRegex()` and `MatchesRegex()` take ownership of the `RE` object. They 103use the regular expression syntax defined 104[here](../advanced.md#regular-expression-syntax). All of these matchers, except 105`ContainsRegex()` and `MatchesRegex()` work for wide strings as well. 106 107## Container Matchers 108 109Most STL-style containers support `==`, so you can use `Eq(expected_container)` 110or simply `expected_container` to match a container exactly. If you want to 111write the elements in-line, match them more flexibly, or get more informative 112messages, you can use: 113 114| Matcher | Description | 115| :---------------------------------------- | :------------------------------- | 116| `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. | 117| `ContainerEq(container)` | The same as `Eq(container)` except that the failure message also includes which elements are in one container but not the other. | 118| `Contains(e)` | `argument` contains an element that matches `e`, which can be either a value or a matcher. | 119| `Each(e)` | `argument` is a container where *every* element matches `e`, which can be either a value or a matcher. | 120| `ElementsAre(e0, e1, ..., en)` | `argument` has `n + 1` elements, where the *i*-th element matches `ei`, which can be a value or a matcher. | 121| `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. | 122| `IsEmpty()` | `argument` is an empty container (`container.empty()`). | 123| `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. | 124| `IsSupersetOf({e0, e1, ..., en})`, `IsSupersetOf(a_container)`, `IsSupersetOf(begin, end)`, `IsSupersetOf(array)`, or `IsSupersetOf(array, count)` | Some subset of `argument` matches `UnorderedElementsAre(`expected matchers`)`. | 125| `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. | 126| `SizeIs(m)` | `argument` is a container whose size matches `m`. E.g. `SizeIs(2)` or `SizeIs(Lt(2))`. | 127| `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. | 128| `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. | 129| `UnorderedPointwise(m, container)`, `UnorderedPointwise(m, {e0, e1, ..., en})` | Like `Pointwise(m, container)`, but ignores the order of elements. | 130| `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. | 131| `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))`. | 132 133**Notes:** 134 135* These matchers can also match: 136 1. a native array passed by reference (e.g. in `Foo(const int (&a)[5])`), 137 and 138 2. an array passed as a pointer and a count (e.g. in `Bar(const T* buffer, 139 int len)` -- see [Multi-argument Matchers](#MultiArgMatchers)). 140* The array being matched may be multi-dimensional (i.e. its elements can be 141 arrays). 142* `m` in `Pointwise(m, ...)` and `UnorderedPointwise(m, ...)` should be a 143 matcher for `::std::tuple<T, U>` where `T` and `U` are the element type of 144 the actual container and the expected container, respectively. For example, 145 to compare two `Foo` containers where `Foo` doesn't support `operator==`, 146 one might write: 147 148 ```cpp 149 using ::std::get; 150 MATCHER(FooEq, "") { 151 return std::get<0>(arg).Equals(std::get<1>(arg)); 152 } 153 ... 154 EXPECT_THAT(actual_foos, Pointwise(FooEq(), expected_foos)); 155 ``` 156 157## Member Matchers 158 159| Matcher | Description | 160| :------------------------------ | :----------------------------------------- | 161| `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_. | 162| `Field(field_name, &class::field, m)` | The same as the two-parameter version, but provides a better error message. | 163| `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`. | 164| `Pair(m1, m2)` | `argument` is an `std::pair` whose `first` field matches `m1` and `second` field matches `m2`. | 165| `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. | 166| `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`. | 167| `Property(property_name, &class::property, m)` | The same as the two-parameter version, but provides a better error message. 168 169**Notes:** 170 171* You can use `FieldsAre()` to match any type that supports structured 172 bindings, such as `std::tuple`, `std::pair`, `std::array`, and aggregate 173 types. For example: 174 175 ```cpp 176 std::tuple<int, std::string> my_tuple{7, "hello world"}; 177 EXPECT_THAT(my_tuple, FieldsAre(Ge(0), HasSubstr("hello"))); 178 179 struct MyStruct { 180 int value = 42; 181 std::string greeting = "aloha"; 182 }; 183 MyStruct s; 184 EXPECT_THAT(s, FieldsAre(42, "aloha")); 185 ``` 186 187* Don't use `Property()` against member functions that you do not own, because 188 taking addresses of functions is fragile and generally not part of the 189 contract of the function. 190 191## Matching the Result of a Function, Functor, or Callback 192 193| Matcher | Description | 194| :--------------- | :------------------------------------------------ | 195| `ResultOf(f, m)` | `f(argument)` matches matcher `m`, where `f` is a function or functor. | 196 197## Pointer Matchers 198 199| Matcher | Description | 200| :------------------------ | :---------------------------------------------- | 201| `Address(m)` | the result of `std::addressof(argument)` matches `m`. | 202| `Pointee(m)` | `argument` (either a smart pointer or a raw pointer) points to a value that matches matcher `m`. | 203| `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`. | 204| `WhenDynamicCastTo<T>(m)` | when `argument` is passed through `dynamic_cast<T>()`, it matches matcher `m`. | 205 206## Multi-argument Matchers {#MultiArgMatchers} 207 208Technically, all matchers match a *single* value. A "multi-argument" matcher is 209just one that matches a *tuple*. The following matchers can be used to match a 210tuple `(x, y)`: 211 212Matcher | Description 213:------ | :---------- 214`Eq()` | `x == y` 215`Ge()` | `x >= y` 216`Gt()` | `x > y` 217`Le()` | `x <= y` 218`Lt()` | `x < y` 219`Ne()` | `x != y` 220 221You can use the following selectors to pick a subset of the arguments (or 222reorder them) to participate in the matching: 223 224| Matcher | Description | 225| :------------------------- | :---------------------------------------------- | 226| `AllArgs(m)` | Equivalent to `m`. Useful as syntactic sugar in `.With(AllArgs(m))`. | 227| `Args<N1, N2, ..., Nk>(m)` | The tuple of the `k` selected (using 0-based indices) arguments matches `m`, e.g. `Args<1, 2>(Eq())`. | 228 229## Composite Matchers 230 231You can make a matcher from one or more other matchers: 232 233| Matcher | Description | 234| :------------------------------- | :-------------------------------------- | 235| `AllOf(m1, m2, ..., mn)` | `argument` matches all of the matchers `m1` to `mn`. | 236| `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. | 237| `AnyOf(m1, m2, ..., mn)` | `argument` matches at least one of the matchers `m1` to `mn`. | 238| `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. | 239| `Not(m)` | `argument` doesn't match matcher `m`. | 240 241## Adapters for Matchers 242 243| Matcher | Description | 244| :---------------------- | :------------------------------------ | 245| `MatcherCast<T>(m)` | casts matcher `m` to type `Matcher<T>`. | 246| `SafeMatcherCast<T>(m)` | [safely casts](../gmock_cook_book.md#SafeMatcherCast) matcher `m` to type `Matcher<T>`. | 247| `Truly(predicate)` | `predicate(argument)` returns something considered by C++ to be true, where `predicate` is a function or functor. | 248 249`AddressSatisfies(callback)` and `Truly(callback)` take ownership of `callback`, 250which must be a permanent callback. 251 252## Using Matchers as Predicates {#MatchersAsPredicatesCheat} 253 254| Matcher | Description | 255| :---------------------------- | :------------------------------------------ | 256| `Matches(m)(value)` | evaluates to `true` if `value` matches `m`. You can use `Matches(m)` alone as a unary functor. | 257| `ExplainMatchResult(m, value, result_listener)` | evaluates to `true` if `value` matches `m`, explaining the result to `result_listener`. | 258| `Value(value, m)` | evaluates to `true` if `value` matches `m`. | 259 260## Defining Matchers 261 262| Matcher | Description | 263| :----------------------------------- | :------------------------------------ | 264| `MATCHER(IsEven, "") { return (arg % 2) == 0; }` | Defines a matcher `IsEven()` to match an even number. | 265| `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`. | 266| `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`]. | 267 268**Notes:** 269 2701. The `MATCHER*` macros cannot be used inside a function or class. 2712. The matcher body must be *purely functional* (i.e. it cannot have any side 272 effect, and the result must not depend on anything other than the value 273 being matched and the matcher parameters). 2743. You can use `PrintToString(x)` to convert a value `x` of any type to a 275 string. 2764. You can use `ExplainMatchResult()` in a custom matcher to wrap another 277 matcher, for example: 278 279 ```cpp 280 MATCHER_P(NestedPropertyMatches, matcher, "") { 281 return ExplainMatchResult(matcher, arg.nested().property(), result_listener); 282 } 283 ``` 284