$z-index: (
  'main',
  'sidebar',
  'banner' 'active-nav' 'dropdown',
  'message',
  'modal',
);


// Z-Index (function)
// ------------------
@include describe('Z-Index [function]') {
  @include it('Simple index list') {
    @include assert-equal(
      z-index('modal'),
      5
    );
  }

  @include it('First item in a nested list') {
    @include assert-equal(
      z-index('banner'),
      3
    );
  }

  @include it('Nested list index') {
    @include assert-equal(
      z-index('active-nav'),
      1
    );

    @include assert-equal(
      z-index('dropdown'),
      2
    );
  }
}


// Z-Index (mixin)
// ---------------
@include describe('Z-Index [mixin]') {
  @include it('Set z-index property') {
    @include assert('Z-Index property is set based on list index') {
      @include output {
        @include z-index('dropdown');
      }

      @include expect {
        z-index: 2;
      }
    }
  }
}