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: 21 22### Wildcard 23 24Matcher | Description 25:-------------------------- | :----------------------------------------------- 26`_` | `argument` can be any value of the correct type. 27`A<type>()` or `An<type>()` | `argument` can be any value of type `type`. 28 29### Generic Comparison 30 31| Matcher | Description | 32| :--------------------- | :-------------------------------------------------- | 33| `Eq(value)` or `value` | `argument == value` | 34| `Ge(value)` | `argument >= value` | 35| `Gt(value)` | `argument > value` | 36| `Le(value)` | `argument <= value` | 37| `Lt(value)` | `argument < value` | 38| `Ne(value)` | `argument != value` | 39| `IsFalse()` | `argument` evaluates to `false` in a Boolean context. | 40| `IsTrue()` | `argument` evaluates to `true` in a Boolean context. | 41| `IsNull()` | `argument` is a `NULL` pointer (raw or smart). | 42| `NotNull()` | `argument` is a non-null pointer (raw or smart). | 43| `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 `==`.)| 44| `VariantWith<T>(m)` | `argument` is `variant<>` that holds the alternative of type T with a value matching `m`. | 45| `Ref(variable)` | `argument` is a reference to `variable`. | 46| `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. | 47 48Except `Ref()`, these matchers make a *copy* of `value` in case it's modified or 49destructed later. If the compiler complains that `value` doesn't have a public 50copy constructor, try wrap it in `std::ref()`, e.g. 51`Eq(std::ref(non_copyable_value))`. If you do that, make sure 52`non_copyable_value` is not changed afterwards, or the meaning of your matcher 53will be changed. 54 55`IsTrue` and `IsFalse` are useful when you need to use a matcher, or for types 56that can be explicitly converted to Boolean, but are not implicitly converted to 57Boolean. In other cases, you can use the basic 58[`EXPECT_TRUE` and `EXPECT_FALSE`](primer.md#basic-assertions) assertions. 59 60### Floating-Point Matchers {#FpMatchers} 61 62| Matcher | Description | 63| :------------------------------- | :--------------------------------- | 64| `DoubleEq(a_double)` | `argument` is a `double` value approximately equal to `a_double`, treating two NaNs as unequal. | 65| `FloatEq(a_float)` | `argument` is a `float` value approximately equal to `a_float`, treating two NaNs as unequal. | 66| `NanSensitiveDoubleEq(a_double)` | `argument` is a `double` value approximately equal to `a_double`, treating two NaNs as equal. | 67| `NanSensitiveFloatEq(a_float)` | `argument` is a `float` value approximately equal to `a_float`, treating two NaNs as equal. | 68| `IsNan()` | `argument` is any floating-point type with a NaN value. | 69 70The above matchers use ULP-based comparison (the same as used in googletest). 71They automatically pick a reasonable error bound based on the absolute value of 72the expected value. `DoubleEq()` and `FloatEq()` conform to the IEEE standard, 73which requires comparing two NaNs for equality to return false. The 74`NanSensitive*` version instead treats two NaNs as equal, which is often what a 75user wants. 76 77| Matcher | Description | 78| :------------------------------------------------ | :----------------------- | 79| `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. | 80| `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. | 81| `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. | 82| `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. | 83 84### String Matchers 85 86The `argument` can be either a C string or a C++ string object: 87 88| Matcher | Description | 89| :---------------------- | :------------------------------------------------- | 90| `ContainsRegex(string)` | `argument` matches the given regular expression. | 91| `EndsWith(suffix)` | `argument` ends with string `suffix`. | 92| `HasSubstr(string)` | `argument` contains `string` as a sub-string. | 93| `IsEmpty()` | `argument` is an empty string. | 94| `MatchesRegex(string)` | `argument` matches the given regular expression with the match starting at the first character and ending at the last character. | 95| `StartsWith(prefix)` | `argument` starts with string `prefix`. | 96| `StrCaseEq(string)` | `argument` is equal to `string`, ignoring case. | 97| `StrCaseNe(string)` | `argument` is not equal to `string`, ignoring case. | 98| `StrEq(string)` | `argument` is equal to `string`. | 99| `StrNe(string)` | `argument` is not equal to `string`. | 100 101`ContainsRegex()` and `MatchesRegex()` take ownership of the `RE` object. They 102use the regular expression syntax defined 103[here](advanced.md#regular-expression-syntax). All of these matchers, except 104`ContainsRegex()` and `MatchesRegex()` work for wide strings as well. 105 106### Container Matchers 107 108Most STL-style containers support `==`, so you can use `Eq(expected_container)` 109or simply `expected_container` to match a container exactly. If you want to 110write the elements in-line, match them more flexibly, or get more informative 111messages, you can use: 112 113| Matcher | Description | 114| :---------------------------------------- | :------------------------------- | 115| `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. | 116| `ContainerEq(container)` | The same as `Eq(container)` except that the failure message also includes which elements are in one container but not the other. | 117| `Contains(e)` | `argument` contains an element that matches `e`, which can be either a value or a matcher. | 118| `Each(e)` | `argument` is a container where *every* element matches `e`, which can be either a value or a matcher. | 119| `ElementsAre(e0, e1, ..., en)` | `argument` has `n + 1` elements, where the *i*-th element matches `ei`, which can be a value or a matcher. | 120| `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. | 121| `IsEmpty()` | `argument` is an empty container (`container.empty()`). | 122| `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. | 123| `IsSupersetOf({e0, e1, ..., en})`, `IsSupersetOf(a_container)`, `IsSupersetOf(begin, end)`, `IsSupersetOf(array)`, or `IsSupersetOf(array, count)` | Some subset of `argument` matches `UnorderedElementsAre(`expected matchers`)`. | 124| `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. | 125| `SizeIs(m)` | `argument` is a container whose size matches `m`. E.g. `SizeIs(2)` or `SizeIs(Lt(2))`. | 126| `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. | 127| `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. | 128| `UnorderedPointwise(m, container)`, `UnorderedPointwise(m, {e0, e1, ..., en})` | Like `Pointwise(m, container)`, but ignores the order of elements. | 129| `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. | 130| `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))`. | 131 132**Notes:** 133 134* These matchers can also match: 135 1. a native array passed by reference (e.g. in `Foo(const int (&a)[5])`), 136 and 137 2. an array passed as a pointer and a count (e.g. in `Bar(const T* buffer, 138 int len)` -- see [Multi-argument Matchers](#MultiArgMatchers)). 139* The array being matched may be multi-dimensional (i.e. its elements can be 140 arrays). 141* `m` in `Pointwise(m, ...)` and `UnorderedPointwise(m, ...)` should be a 142 matcher for `::std::tuple<T, U>` where `T` and `U` are the element type of 143 the actual container and the expected container, respectively. For example, 144 to compare two `Foo` containers where `Foo` doesn't support `operator==`, 145 one might write: 146 147 ```cpp 148 using ::std::get; 149 MATCHER(FooEq, "") { 150 return std::get<0>(arg).Equals(std::get<1>(arg)); 151 } 152 ... 153 EXPECT_THAT(actual_foos, Pointwise(FooEq(), expected_foos)); 154 ``` 155 156### Member Matchers 157 158| Matcher | Description | 159| :------------------------------ | :----------------------------------------- | 160| `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_. | 161| `Field(field_name, &class::field, m)` | The same as the two-parameter version, but provides a better error message. | 162| `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`. | 163| `Pair(m1, m2)` | `argument` is an `std::pair` whose `first` field matches `m1` and `second` field matches `m2`. | 164| `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. | 165| `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`. | 166| `Property(property_name, &class::property, m)` | The same as the two-parameter version, but provides a better error message. 167 168**Notes:** 169 170* You can use `FieldsAre()` to match any type that supports structured 171 bindings, such as `std::tuple`, `std::pair`, `std::array`, and aggregate 172 types. For example: 173 174 ```cpp 175 std::tuple<int, std::string> my_tuple{7, "hello world"}; 176 EXPECT_THAT(my_tuple, FieldsAre(Ge(0), HasSubstr("hello"))); 177 178 struct MyStruct { 179 int value = 42; 180 std::string greeting = "aloha"; 181 }; 182 MyStruct s; 183 EXPECT_THAT(s, FieldsAre(42, "aloha")); 184 ``` 185 186* Don't use `Property()` against member functions that you do not own, because 187 taking addresses of functions is fragile and generally not part of the 188 contract of the function. 189 190### Matching the Result of a Function, Functor, or Callback 191 192| Matcher | Description | 193| :--------------- | :------------------------------------------------ | 194| `ResultOf(f, m)` | `f(argument)` matches matcher `m`, where `f` is a function or functor. | 195 196### Pointer Matchers 197 198| Matcher | Description | 199| :------------------------ | :---------------------------------------------- | 200| `Address(m)` | the result of `std::addressof(argument)` matches `m`. | 201| `Pointee(m)` | `argument` (either a smart pointer or a raw pointer) points to a value that matches matcher `m`. | 202| `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`. | 203| `WhenDynamicCastTo<T>(m)` | when `argument` is passed through `dynamic_cast<T>()`, it matches matcher `m`. | 204 205### Multi-argument Matchers {#MultiArgMatchers} 206 207Technically, all matchers match a *single* value. A "multi-argument" matcher is 208just one that matches a *tuple*. The following matchers can be used to match a 209tuple `(x, y)`: 210 211Matcher | Description 212:------ | :---------- 213`Eq()` | `x == y` 214`Ge()` | `x >= y` 215`Gt()` | `x > y` 216`Le()` | `x <= y` 217`Lt()` | `x < y` 218`Ne()` | `x != y` 219 220You can use the following selectors to pick a subset of the arguments (or 221reorder them) to participate in the matching: 222 223| Matcher | Description | 224| :------------------------- | :---------------------------------------------- | 225| `AllArgs(m)` | Equivalent to `m`. Useful as syntactic sugar in `.With(AllArgs(m))`. | 226| `Args<N1, N2, ..., Nk>(m)` | The tuple of the `k` selected (using 0-based indices) arguments matches `m`, e.g. `Args<1, 2>(Eq())`. | 227 228### Composite Matchers 229 230You can make a matcher from one or more other matchers: 231 232| Matcher | Description | 233| :------------------------------- | :-------------------------------------- | 234| `AllOf(m1, m2, ..., mn)` | `argument` matches all of the matchers `m1` to `mn`. | 235| `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. | 236| `AnyOf(m1, m2, ..., mn)` | `argument` matches at least one of the matchers `m1` to `mn`. | 237| `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. | 238| `Not(m)` | `argument` doesn't match matcher `m`. | 239 240### Adapters for Matchers 241 242| Matcher | Description | 243| :---------------------- | :------------------------------------ | 244| `MatcherCast<T>(m)` | casts matcher `m` to type `Matcher<T>`. | 245| `SafeMatcherCast<T>(m)` | [safely casts](gmock_cook_book.md#casting-matchers) matcher `m` to type `Matcher<T>`. | 246| `Truly(predicate)` | `predicate(argument)` returns something considered by C++ to be true, where `predicate` is a function or functor. | 247 248`AddressSatisfies(callback)` and `Truly(callback)` take ownership of `callback`, 249which must be a permanent callback. 250 251### Using Matchers as Predicates {#MatchersAsPredicatesCheat} 252 253| Matcher | Description | 254| :---------------------------- | :------------------------------------------ | 255| `Matches(m)(value)` | evaluates to `true` if `value` matches `m`. You can use `Matches(m)` alone as a unary functor. | 256| `ExplainMatchResult(m, value, result_listener)` | evaluates to `true` if `value` matches `m`, explaining the result to `result_listener`. | 257| `Value(value, m)` | evaluates to `true` if `value` matches `m`. | 258 259### Defining Matchers 260 261| Matcher | Description | 262| :----------------------------------- | :------------------------------------ | 263| `MATCHER(IsEven, "") { return (arg % 2) == 0; }` | Defines a matcher `IsEven()` to match an even number. | 264| `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`. | 265| `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`]. | 266 267**Notes:** 268 2691. The `MATCHER*` macros cannot be used inside a function or class. 2702. The matcher body must be *purely functional* (i.e. it cannot have any side 271 effect, and the result must not depend on anything other than the value 272 being matched and the matcher parameters). 2733. You can use `PrintToString(x)` to convert a value `x` of any type to a 274 string. 2754. You can use `ExplainMatchResult()` in a custom matcher to wrap another 276 matcher, for example: 277 278 ```cpp 279 MATCHER_P(NestedPropertyMatches, matcher, "") { 280 return ExplainMatchResult(matcher, arg.nested().property(), result_listener); 281 } 282 ``` 283