// Assert
// ======

@mixin assert-true(
  $assert,
  $fail-message: null
) {
  $default-message: '(#{$assert} is not true)';
  $fail-message: join($fail-message, $default-message, space);
  @if $assert { @include pass; }
  @else { @include fail($fail-message); }
}

@mixin assert-false(
  $assert,
  $fail-message: null
) {
  $default-message: '(#{$assert} is not false)';
  $fail-message: join($fail-message, $default-message, space);
  @if not $assert { @include pass; }
  @else { @include fail($fail-message); }
}

@mixin assert-equal(
  $assert,
  $expected,
  $fail-message: null
) {
  $default-message: '(#{$assert} != #{$expected})';
  $fail-message: join($fail-message, $default-message, space);
  @if $assert == $expected { @include pass; }
  @else { @include fail($fail-message); }
}

@mixin assert-unequal(
  $assert,
  $expected,
  $fail-message: null
) {
  $default-message: '(#{$assert} == #{$expected})';
  $fail-message: join($fail-message, $default-message, space);
  @if $assert != $expected { @include pass; }
  @else { @include fail($fail-message); }
}

// Assert
// ======

@mixin assert-true(
  $assert,
  $fail-message: null
) {
  $default-message: ' (#{$assert} is not true)';
  $fail-message: $fail-message + $default-message;
  @if $assert { @include pass; }
  @else { @include fail($fail-message); }
}

@mixin assert-false(
  $assert,
  $fail-message: null
) {
  $default-message: ' (#{$assert} is not false)';
  $fail-message: $fail-message + $default-message;
  @if not $assert { @include pass; }
  @else { @include fail($fail-message); }
}

@mixin assert-equal(
  $assert,
  $expected,
  $fail-message: null
) {
  $default-message: ' (#{$assert} != #{$expected})';
  $fail-message: $fail-message + $default-message;
  @if $assert == $expected { @include pass; }
  @else { @include fail($fail-message); }
}

@mixin assert-unequal(
  $assert,
  $expected,
  $fail-message: null
) {
  $default-message: ' (#{$assert} == #{$expected})';
  $fail-message: $fail-message + $default-message;
  @if $assert != $expected { @include pass; }
  @else { @include fail($fail-message); }
}

Add strings, rather than using list
Add strings, rather than using list
