@include test('_format(..)') {
  $tests: (
    (1, 2, 3): '1.2.3',
    (1, 2, 3, 'foobar'): '1.2.3',
    (1, 2, 3, 'foobar', 42): '1.2.3-foobar.42',
  );

  @each $test, $expect in $tests {
    @include assert-equal(_format($test...), $expect, 'Format a version from its components.');
  }
}