catch2/docs/logging.md

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# Logging macros

Additional messages can be logged during a test case. Note that the messages are scoped and thus will not be reported if failure occurs in scope preceding the message declaration. An example:

```cpp
TEST_CASE("Foo") {
    INFO("Test case start");
    for (int i = 0; i < 2; ++i) {
        INFO("The number is " << i);
        CHECK(i == 0);
    }
}

TEST_CASE("Bar") {
    INFO("Test case start");
    for (int i = 0; i < 2; ++i) {
        INFO("The number is " << i);
        CHECK(i == i);
    }
    CHECK(false);
}
```
When the `CHECK` fails in the "Foo" test case, then two messages will be printed.
```
Test case start
The number is 1
```
When the last `CHECK` fails in the "Bar" test case, then only one message will be printed: `Test case start`.


## Streaming macros

All these macros allow heterogenous sequences of values to be streaming using the insertion operator (```<<```) in the same way that std::ostream, std::cout, etc support it.

E.g.:
```c++
INFO( "The number is " << i );
```

(Note that there is no initial ```<<``` - instead the insertion sequence is placed in parentheses.)
These macros come in three forms:

**INFO(** _message expression_ **)**

The message is logged to a buffer, but only reported with the next assertion that is logged. This allows you to log contextual information in case of failures which is not shown during a successful test run (for the console reporter, without -s). Messages are removed from the buffer at the end of their scope, so may be used, for example, in loops.

_Note that in Catch2 2.x.x `INFO` can be used without a trailing semicolon as there is a trailing semicolon inside macro.
This semicolon will be removed with next major version. It is highly advised to use a trailing semicolon after `INFO` macro._

**WARN(** _message expression_ **)**

The message is always reported but does not fail the test.

**FAIL(** _message expression_ **)**

The message is reported and the test case fails.

**FAIL_CHECK(** _message expression_ **)**

AS `FAIL`, but does not abort the test

## Quickly capture value of variables or expressions

**CAPTURE(** _expression1_, _expression2_, ... **)**

Sometimes you just want to log a value of variable, or expression. For
convenience, we provide the `CAPTURE` macro, that can take a variable,
or an expression, and prints out that variable/expression and its value
at the time of capture.

e.g. `CAPTURE( theAnswer );` will log message "theAnswer := 42", while
```cpp
int a = 1, b = 2, c = 3;
CAPTURE( a, b, c, a + b, c > b, a == 1);
```
will log a total of 6 messages:
```
a := 1
b := 2
c := 3
a + b := 3
c > b := true
a == 1 := true
```

You can also capture expressions that use commas inside parentheses
(e.g. function calls), brackets, or braces (e.g. initializers). To
properly capture expression that contains template parameters list
(in other words, it contains commas between angle brackets), you need
to enclose the expression inside parentheses:
`CAPTURE( (std::pair<int, int>{1, 2}) );`


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