@include test('_prerelease(..)') {
  $tests: (
    '1.2.3': ( 'name': null, 'number': -1 ),
    '1.2.3-alpha': ( 'name': 'alpha', 'number': -1 ),
    '1.2.3-alpha.beta': ( 'name': 'alpha.beta', 'number': -1 ),
    '1.2.3-alpha.beta.42': ( 'name': 'alpha.beta', 'number': 42 ),
    '1.2.3-alpha.0': ( 'name': 'alpha', 'number': 0 ),
    '1.2.3-0': ( 'name': null, 'number': 0 ),
  );

  @each $test, $expect in $tests {
    @include assert-equal(_prerelease($test), $expect, 'Parse the prerelease of a version.');
  }
}