Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.3.4)
// Compass (v1.0.0.alpha.18)
// ----

$default: 1;

@mixin test($p: "no arguments have been passed, and if someone is going to pass this exact extremely long string, they better hide") {
    @if ($p == "no arguments have been passed, and if someone is going to pass this exact extremely long string, they better hide") {
      $p: $default;
      /* Do something if $p is NOT passed */
      value: $p;
    } @else {
      /* Do something else if $p is passed */
      value: $p;
    }
}

test1 {
  @include test();
}
test2 {
  @include test(null);
}

SassMeister-output.css

test1 {
  /* Do something if $p is NOT passed */
  value: 1;
}

test2 {
  /* Do something else if $p is passed */
}