assert is the testing library included with Brat. It works by setting up a series of tests, which include one or more assertions. Then it runs all the tests and collects the results. Each test is given a name so it can be reported when a test fails.

The basic usage looks like this:

include :assert

setup {
  test "addition" {
    assert_equal 5 { 2 + 2 }

The output from running the code above looks like this:

Loading tests...
Running tests...
(1/1) addition                                
Test failure(s):

        1. 'addition': expected 5, but was 4

1 tests, 1 assertions, 1 failures.