A proof of concept I created in Sept of 2012 showing how unit testing of SCSS code could work. This code was runnable, or close to it, with a runner I wrote, but is not in good enough shape to post.

sass-tester-example.scss

@import "../base/functions";
$base-size: 10px;

@function to-equal($actual, $expected){
  @if $expected == $actual {
    @return true;
  } @else {
    @return $actual;
  }
}

@function to-almost-equal($actual, $expected, $variance: .5){
  @if $actual - $expected <= $variance {
    @return true;
  } @else {
    @return $actual;
  }
}

strip-units {
  remove-from-em {
    expect: to-equal(strip-units(1em), 1);
  }
}

to-px {
  basic-conversion {
    expect: to-equal(to-px(1em), 10px);
  }
}

to-em {
  basic-conversion {
    expect: to-equal(to-em(10px), 1em);
  }

  convert-with-em-context {
    expect: to-equal(to-em(10px, 2em), .5em);
  }

  convert-with-em-context-messy {
    expect: to-almost-equal(to-em(14px, 3em), .46667em);
  }

  convert-with-px-context {
    expect: to-equal(to-em(10px, 20px), .5em);
  }
}