catch2/docs/logging.md

Logging macros

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

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.

Logging without local scope

Introduced in Catch2 2.7.0.

UNSCOPED_INFO is similar to INFO with two key differences:

• Lifetime of an unscoped message is not tied to its own scope.
• An unscoped message can be reported by the first following assertion only, regardless of the result of that assertion.

In other words, lifetime of UNSCOPED_INFO is limited by the following assertion (or by the end of test case/section, whichever comes first) whereas lifetime of INFO is limited by its own scope.

These differences make this macro useful for reporting information from helper functions or inner scopes. An example:

void print_some_info() {
    UNSCOPED_INFO("Info from helper");
}

TEST_CASE("Baz") {
    print_some_info();
    for (int i = 0; i < 2; ++i) {
        UNSCOPED_INFO("The number is " << i);
    }
    CHECK(false);
}

TEST_CASE("Qux") {
    INFO("First info");
    UNSCOPED_INFO("First unscoped info");
    CHECK(false);

    INFO("Second info");
    UNSCOPED_INFO("Second unscoped info");
    CHECK(false);
}

"Baz" test case prints:

Info from helper
The number is 0
The number is 1

With "Qux" test case, two messages will be printed when the first CHECK fails:

First info
First unscoped info

"First unscoped info" message will be cleared after the first CHECK, while "First info" message will persist until the end of the test case. Therefore, when the second CHECK fails, three messages will be printed:

First info
Second info
Second unscoped info

Streaming macros

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

E.g.:

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 next assertions that are 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.

UNSCOPED_INFO( message expression )

Introduced in Catch2 2.7.0.

Similar to INFO, but messages are not limited to their own scope: They are removed from the buffer after each assertion, section or test case, whichever comes first.

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

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}) );