assert2

assert!(...) and check!(...) macros inspired by Catch2.

This crate is currently a work in progress. It relies on a nightly compiler with the proc_macro_hygiene, proc_macro_span and specialization features. As a user of the crate, you also need to enable the proc_macro_hygiene feature.

Unlike the asserts in standard library, there is no difference between assert, assert_eq or others. Instead, you write all checks with the same assert!(...) or check!(...) macros. The macros recognize what kind of expression you wrote and will provide a useful error message with colored output when the check fails.

Also unlike the standard std::assert, the macros from this crate show both the original expression and the value of the expression. The standard library asserts only show the value of the expression.

Finally, in addition to boolean expressions, you can test if a value matches a pattern by putting a let expression in the macro. A quick example:

check!(6 == 2 * 3);
check!(true || false);
check!(let Err(_) = File::open("/non/existing/file"));

Sample output

check!(6 + 1 <= 2 * 3);

check!(true && false);

check!(let Ok(_) = File::open("/non/existing/file"));

assert vs check

The crate provides two macros: check!(...) and assert!(...). The main difference is that check doesn't immediately panic. Instead, it will print the assertion error and fail the test. This allows you to run multiple checks, and can help to paint a clearer picture why a test failed.

Currently, check uses a scope guard to delay the panic until the current scope ends. Ideally, check should not panic until the whole test body has finished. Even better would be if check doesn't panic at all, but simply marks the test as failed. If this becomes possible in the future, the check macro will change, so you should not rely on check to panic.

Controlling colors.

You can force colored output on or off by setting the CLICOLOR environment variable. Set CLICOLOR=1 to forcibly enable colors, or CLICOLORS=0 to disable them. If the environment variable is unset or set to auto, output will be colored if it is going to a terminal.