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283 lines
19 KiB
# Matchers Reference
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A **matcher** matches a *single* argument. You can use it inside `ON_CALL()` or
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`EXPECT_CALL()`, or use it to validate a value directly using two macros:
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| Macro | Description |
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| :----------------------------------- | :------------------------------------ |
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| `EXPECT_THAT(actual_value, matcher)` | Asserts that `actual_value` matches `matcher`. |
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| `ASSERT_THAT(actual_value, matcher)` | The same as `EXPECT_THAT(actual_value, matcher)`, except that it generates a **fatal** failure. |
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{: .callout .note}
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**Note:** Although equality matching via `EXPECT_THAT(actual_value,
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expected_value)` is supported, prefer to make the comparison explicit via
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`EXPECT_THAT(actual_value, Eq(expected_value))` or `EXPECT_EQ(actual_value,
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expected_value)`.
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Built-in matchers (where `argument` is the function argument, e.g.
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`actual_value` in the example above, or when used in the context of
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`EXPECT_CALL(mock_object, method(matchers))`, the arguments of `method`) are
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divided into several categories:
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### Wildcard
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Matcher | Description
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:-------------------------- | :-----------------------------------------------
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`_` | `argument` can be any value of the correct type.
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`A<type>()` or `An<type>()` | `argument` can be any value of type `type`.
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### Generic Comparison
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| Matcher | Description |
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| :--------------------- | :-------------------------------------------------- |
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| `Eq(value)` or `value` | `argument == value` |
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| `Ge(value)` | `argument >= value` |
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| `Gt(value)` | `argument > value` |
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| `Le(value)` | `argument <= value` |
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| `Lt(value)` | `argument < value` |
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| `Ne(value)` | `argument != value` |
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| `IsFalse()` | `argument` evaluates to `false` in a Boolean context. |
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| `IsTrue()` | `argument` evaluates to `true` in a Boolean context. |
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| `IsNull()` | `argument` is a `NULL` pointer (raw or smart). |
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| `NotNull()` | `argument` is a non-null pointer (raw or smart). |
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| `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 `==`.)|
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| `VariantWith<T>(m)` | `argument` is `variant<>` that holds the alternative of type T with a value matching `m`. |
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| `Ref(variable)` | `argument` is a reference to `variable`. |
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| `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. |
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Except `Ref()`, these matchers make a *copy* of `value` in case it's modified or
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destructed later. If the compiler complains that `value` doesn't have a public
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copy constructor, try wrap it in `std::ref()`, e.g.
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`Eq(std::ref(non_copyable_value))`. If you do that, make sure
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`non_copyable_value` is not changed afterwards, or the meaning of your matcher
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will be changed.
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`IsTrue` and `IsFalse` are useful when you need to use a matcher, or for types
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that can be explicitly converted to Boolean, but are not implicitly converted to
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Boolean. In other cases, you can use the basic
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[`EXPECT_TRUE` and `EXPECT_FALSE`](primer.md#basic-assertions) assertions.
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### Floating-Point Matchers {#FpMatchers}
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| Matcher | Description |
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| :------------------------------- | :--------------------------------- |
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| `DoubleEq(a_double)` | `argument` is a `double` value approximately equal to `a_double`, treating two NaNs as unequal. |
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| `FloatEq(a_float)` | `argument` is a `float` value approximately equal to `a_float`, treating two NaNs as unequal. |
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| `NanSensitiveDoubleEq(a_double)` | `argument` is a `double` value approximately equal to `a_double`, treating two NaNs as equal. |
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| `NanSensitiveFloatEq(a_float)` | `argument` is a `float` value approximately equal to `a_float`, treating two NaNs as equal. |
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| `IsNan()` | `argument` is any floating-point type with a NaN value. |
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The above matchers use ULP-based comparison (the same as used in googletest).
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They automatically pick a reasonable error bound based on the absolute value of
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the expected value. `DoubleEq()` and `FloatEq()` conform to the IEEE standard,
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which requires comparing two NaNs for equality to return false. The
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`NanSensitive*` version instead treats two NaNs as equal, which is often what a
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user wants.
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| Matcher | Description |
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| :------------------------------------------------ | :----------------------- |
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| `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. |
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| `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. |
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| `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. |
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| `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. |
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### String Matchers
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The `argument` can be either a C string or a C++ string object:
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| Matcher | Description |
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| :---------------------- | :------------------------------------------------- |
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| `ContainsRegex(string)` | `argument` matches the given regular expression. |
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| `EndsWith(suffix)` | `argument` ends with string `suffix`. |
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| `HasSubstr(string)` | `argument` contains `string` as a sub-string. |
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| `IsEmpty()` | `argument` is an empty string. |
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| `MatchesRegex(string)` | `argument` matches the given regular expression with the match starting at the first character and ending at the last character. |
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| `StartsWith(prefix)` | `argument` starts with string `prefix`. |
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| `StrCaseEq(string)` | `argument` is equal to `string`, ignoring case. |
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| `StrCaseNe(string)` | `argument` is not equal to `string`, ignoring case. |
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| `StrEq(string)` | `argument` is equal to `string`. |
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| `StrNe(string)` | `argument` is not equal to `string`. |
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`ContainsRegex()` and `MatchesRegex()` take ownership of the `RE` object. They
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use the regular expression syntax defined
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[here](advanced.md#regular-expression-syntax). All of these matchers, except
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`ContainsRegex()` and `MatchesRegex()` work for wide strings as well.
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### Container Matchers
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Most STL-style containers support `==`, so you can use `Eq(expected_container)`
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or simply `expected_container` to match a container exactly. If you want to
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write the elements in-line, match them more flexibly, or get more informative
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messages, you can use:
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| Matcher | Description |
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| :---------------------------------------- | :------------------------------- |
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| `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. |
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| `ContainerEq(container)` | The same as `Eq(container)` except that the failure message also includes which elements are in one container but not the other. |
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| `Contains(e)` | `argument` contains an element that matches `e`, which can be either a value or a matcher. |
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| `Each(e)` | `argument` is a container where *every* element matches `e`, which can be either a value or a matcher. |
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| `ElementsAre(e0, e1, ..., en)` | `argument` has `n + 1` elements, where the *i*-th element matches `ei`, which can be a value or a matcher. |
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| `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. |
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| `IsEmpty()` | `argument` is an empty container (`container.empty()`). |
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| `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. |
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| `IsSupersetOf({e0, e1, ..., en})`, `IsSupersetOf(a_container)`, `IsSupersetOf(begin, end)`, `IsSupersetOf(array)`, or `IsSupersetOf(array, count)` | Some subset of `argument` matches `UnorderedElementsAre(`expected matchers`)`. |
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| `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. |
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| `SizeIs(m)` | `argument` is a container whose size matches `m`. E.g. `SizeIs(2)` or `SizeIs(Lt(2))`. |
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| `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. |
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| `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. |
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| `UnorderedPointwise(m, container)`, `UnorderedPointwise(m, {e0, e1, ..., en})` | Like `Pointwise(m, container)`, but ignores the order of elements. |
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| `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. |
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| `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))`. |
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**Notes:**
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* These matchers can also match:
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1. a native array passed by reference (e.g. in `Foo(const int (&a)[5])`),
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and
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2. an array passed as a pointer and a count (e.g. in `Bar(const T* buffer,
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int len)` -- see [Multi-argument Matchers](#MultiArgMatchers)).
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* The array being matched may be multi-dimensional (i.e. its elements can be
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arrays).
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* `m` in `Pointwise(m, ...)` and `UnorderedPointwise(m, ...)` should be a
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matcher for `::std::tuple<T, U>` where `T` and `U` are the element type of
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the actual container and the expected container, respectively. For example,
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to compare two `Foo` containers where `Foo` doesn't support `operator==`,
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one might write:
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```cpp
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using ::std::get;
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MATCHER(FooEq, "") {
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return std::get<0>(arg).Equals(std::get<1>(arg));
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}
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...
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EXPECT_THAT(actual_foos, Pointwise(FooEq(), expected_foos));
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```
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### Member Matchers
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| Matcher | Description |
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| :------------------------------ | :----------------------------------------- |
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| `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_. |
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| `Field(field_name, &class::field, m)` | The same as the two-parameter version, but provides a better error message. |
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| `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`. |
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| `Pair(m1, m2)` | `argument` is an `std::pair` whose `first` field matches `m1` and `second` field matches `m2`. |
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| `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. |
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| `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`. |
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| `Property(property_name, &class::property, m)` | The same as the two-parameter version, but provides a better error message.
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**Notes:**
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* You can use `FieldsAre()` to match any type that supports structured
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bindings, such as `std::tuple`, `std::pair`, `std::array`, and aggregate
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types. For example:
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```cpp
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std::tuple<int, std::string> my_tuple{7, "hello world"};
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EXPECT_THAT(my_tuple, FieldsAre(Ge(0), HasSubstr("hello")));
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struct MyStruct {
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int value = 42;
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std::string greeting = "aloha";
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};
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MyStruct s;
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EXPECT_THAT(s, FieldsAre(42, "aloha"));
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```
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* Don't use `Property()` against member functions that you do not own, because
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taking addresses of functions is fragile and generally not part of the
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contract of the function.
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### Matching the Result of a Function, Functor, or Callback
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| Matcher | Description |
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| :--------------- | :------------------------------------------------ |
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| `ResultOf(f, m)` | `f(argument)` matches matcher `m`, where `f` is a function or functor. |
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### Pointer Matchers
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| Matcher | Description |
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| :------------------------ | :---------------------------------------------- |
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| `Address(m)` | the result of `std::addressof(argument)` matches `m`. |
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| `Pointee(m)` | `argument` (either a smart pointer or a raw pointer) points to a value that matches matcher `m`. |
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| `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`. |
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| `WhenDynamicCastTo<T>(m)` | when `argument` is passed through `dynamic_cast<T>()`, it matches matcher `m`. |
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### Multi-argument Matchers {#MultiArgMatchers}
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Technically, all matchers match a *single* value. A "multi-argument" matcher is
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just one that matches a *tuple*. The following matchers can be used to match a
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tuple `(x, y)`:
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Matcher | Description
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:------ | :----------
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`Eq()` | `x == y`
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`Ge()` | `x >= y`
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`Gt()` | `x > y`
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`Le()` | `x <= y`
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`Lt()` | `x < y`
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`Ne()` | `x != y`
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You can use the following selectors to pick a subset of the arguments (or
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reorder them) to participate in the matching:
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| Matcher | Description |
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| :------------------------- | :---------------------------------------------- |
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| `AllArgs(m)` | Equivalent to `m`. Useful as syntactic sugar in `.With(AllArgs(m))`. |
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| `Args<N1, N2, ..., Nk>(m)` | The tuple of the `k` selected (using 0-based indices) arguments matches `m`, e.g. `Args<1, 2>(Eq())`. |
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### Composite Matchers
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You can make a matcher from one or more other matchers:
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| Matcher | Description |
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| :------------------------------- | :-------------------------------------- |
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| `AllOf(m1, m2, ..., mn)` | `argument` matches all of the matchers `m1` to `mn`. |
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| `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. |
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| `AnyOf(m1, m2, ..., mn)` | `argument` matches at least one of the matchers `m1` to `mn`. |
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| `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. |
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| `Not(m)` | `argument` doesn't match matcher `m`. |
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### Adapters for Matchers
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| Matcher | Description |
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| :---------------------- | :------------------------------------ |
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| `MatcherCast<T>(m)` | casts matcher `m` to type `Matcher<T>`. |
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| `SafeMatcherCast<T>(m)` | [safely casts](gmock_cook_book.md#casting-matchers) matcher `m` to type `Matcher<T>`. |
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| `Truly(predicate)` | `predicate(argument)` returns something considered by C++ to be true, where `predicate` is a function or functor. |
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`AddressSatisfies(callback)` and `Truly(callback)` take ownership of `callback`,
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which must be a permanent callback.
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### Using Matchers as Predicates {#MatchersAsPredicatesCheat}
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| Matcher | Description |
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| :---------------------------- | :------------------------------------------ |
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| `Matches(m)(value)` | evaluates to `true` if `value` matches `m`. You can use `Matches(m)` alone as a unary functor. |
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| `ExplainMatchResult(m, value, result_listener)` | evaluates to `true` if `value` matches `m`, explaining the result to `result_listener`. |
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| `Value(value, m)` | evaluates to `true` if `value` matches `m`. |
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### Defining Matchers
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| Matcher | Description |
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| :----------------------------------- | :------------------------------------ |
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| `MATCHER(IsEven, "") { return (arg % 2) == 0; }` | Defines a matcher `IsEven()` to match an even number. |
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| `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`. |
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| `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`]. |
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**Notes:**
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1. The `MATCHER*` macros cannot be used inside a function or class.
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2. The matcher body must be *purely functional* (i.e. it cannot have any side
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effect, and the result must not depend on anything other than the value
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being matched and the matcher parameters).
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3. You can use `PrintToString(x)` to convert a value `x` of any type to a
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string.
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4. You can use `ExplainMatchResult()` in a custom matcher to wrap another
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matcher, for example:
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```cpp
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MATCHER_P(NestedPropertyMatches, matcher, "") {
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return ExplainMatchResult(matcher, arg.nested().property(), result_listener);
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}
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```
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