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Add example using EXPECT statement in custom matcher
`EXPECT_...` statements can be used inside matcher definitions – this is an important option that is glossed over in this documentation. Users should definitely be aware of this option, since writing custom messages to the `result_listener` can be very cumbersome (and unnecessary) sometimes. This change adds a relevant example and includes the associated error message it provides on failure. PiperOrigin-RevId: 630206661 Change-Id: Idee00ba77ce3c1245597aa082f9cd0efff16aceb
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@ -3312,7 +3312,7 @@ For convenience, we allow the description string to be empty (`""`), in which
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case gMock will use the sequence of words in the matcher name as the
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description.
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For example:
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#### Basic Example
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```cpp
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MATCHER(IsDivisibleBy7, "") { return (arg % 7) == 0; }
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@ -3350,6 +3350,8 @@ If the above assertions fail, they will print something like:
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where the descriptions `"is divisible by 7"` and `"not (is divisible by 7)"` are
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automatically calculated from the matcher name `IsDivisibleBy7`.
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#### Adding Custom Failure Messages
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As you may have noticed, the auto-generated descriptions (especially those for
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the negation) may not be so great. You can always override them with a `string`
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expression of your own:
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@ -3383,14 +3385,41 @@ With this definition, the above assertion will give a better message:
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Actual: 27 (the remainder is 6)
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```
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#### Using EXPECT_ Statements in Matchers
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You can also use `EXPECT_...` (and `ASSERT_...`) statements inside custom
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matcher definitions. In many cases, this allows you to write your matcher more
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concisely while still providing an informative error message. For example:
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```cpp
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MATCHER(IsDivisibleBy7, "") {
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const auto remainder = arg % 7;
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EXPECT_EQ(remainder, 0);
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return true;
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}
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```
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If you write a test that includes the line `EXPECT_THAT(27, IsDivisibleBy7());`,
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you will get an error something like the following:
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```shell
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Expected equality of these values:
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remainder
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Which is: 6
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0
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```
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#### `MatchAndExplain`
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You should let `MatchAndExplain()` print *any additional information* that can
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help a user understand the match result. Note that it should explain why the
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match succeeds in case of a success (unless it's obvious) - this is useful when
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the matcher is used inside `Not()`. There is no need to print the argument value
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itself, as gMock already prints it for you.
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{: .callout .note}
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NOTE: The type of the value being matched (`arg_type`) is determined by the
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#### Argument Types
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The type of the value being matched (`arg_type`) is determined by the
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context in which you use the matcher and is supplied to you by the compiler, so
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you don't need to worry about declaring it (nor can you). This allows the
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matcher to be polymorphic. For example, `IsDivisibleBy7()` can be used to match
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