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Update explanation of REQUIRE_FALSE in docs/assertions.md

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Martin Hořeňovský 2022-10-17 15:13:00 +02:00
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@ -3,6 +3,7 @@
**Contents**<br> **Contents**<br>
[Natural Expressions](#natural-expressions)<br> [Natural Expressions](#natural-expressions)<br>
[Floating point comparisons](#floating-point-comparisons)<br>
[Exceptions](#exceptions)<br> [Exceptions](#exceptions)<br>
[Matcher expressions](#matcher-expressions)<br> [Matcher expressions](#matcher-expressions)<br>
[Thread Safety](#thread-safety)<br> [Thread Safety](#thread-safety)<br>
@ -31,16 +32,26 @@ CHECK( thisReturnsTrue() );
REQUIRE( i == 42 ); REQUIRE( i == 42 );
``` ```
Expressions prefixed with `!` cannot be decomposed. If you have a type
that is convertible to bool and you want to assert that it evaluates to
false, use the two forms below:
* **REQUIRE_FALSE(** _expression_ **)** and * **REQUIRE_FALSE(** _expression_ **)** and
* **CHECK_FALSE(** _expression_ **)** * **CHECK_FALSE(** _expression_ **)**
Evaluates the expression and records the _logical NOT_ of the result. If an exception is thrown it is caught, reported, and counted as a failure. Note that there is no reason to use these forms for plain bool variables,
(these forms exist as a workaround for the fact that `!` prefixed expressions cannot be decomposed). because there is no added value in decomposing them.
Example: Example:
```cpp
Status ret = someFunction();
REQUIRE_FALSE(ret); // ret must evaluate to false, and Catch2 will print
// out the value of ret if possibly
``` ```
REQUIRE_FALSE( thisReturnsFalse() );
```
### Other limitations
Note that expressions containing either of the binary logical operators, Note that expressions containing either of the binary logical operators,
`&&` or `||`, cannot be decomposed and will not compile. The reason behind `&&` or `||`, cannot be decomposed and will not compile. The reason behind
@ -69,7 +80,7 @@ options.
your tests. your tests.
### Floating point comparisons ## Floating point comparisons
Comparing floating point numbers is complex, and [so it has its own Comparing floating point numbers is complex, and [so it has its own
documentation page](comparing-floating-point-numbers.md#top). documentation page](comparing-floating-point-numbers.md#top).