@mixin A($width: 0, $height: 0, $opacity: 0) {
  width: $width;
  height: $height;
  opacity: $opacity;
}

@mixin B($args...) {
  @include A($args...);
}

@mixin C($args...) {
  @include B($args...);
}

.testOneLevelPassthrough {
  @include B(1px, 2px, 0.3);
}

.testOneLevelNoArgs {
  @include B();
}

.testOneLevelSingleArg {
  @include B(1px);
}

.testOneLevelNamedSingleArg {
  @include B($opacity: 0.1);
}

.testOneLevelNamedArgs {
  @include B($opacity: 0.3, $width: 1px, $height: 2px);
}

.testTwoLevelPassthrough {
  @include C(1px, 2px, 0.3);
}

.testTwoLevelNoArgs {
  @include C();
}

.testTwoLevelSingleArg {
  @include C(1px);
}

.testTwoLevelNamedSingleArg {
  @include C($opacity: 0.1);
}

.testTwoLevelNamedArgs {
  @include C($opacity: 0.3, $width: 1px, $height: 2px);
}