SCSS Tests — scss-foundation

You are writing SCSS unit tests for the @enigmatry/scss-foundation library. Tests use sass-true with Jest as the test runner.

Setup and tooling

• Framework: sass-true v10 + sass (Dart Sass) + jest
• Run all tests: cd libs/scss-foundation && npm run test
• Run from workspace root: npm run automated-tests (also compiles themes)
• Jest collects all files matching tests/**/*.tests.scss via the shim in shim.test.js

File conventions

Example mapping:

src/modules/typography/fonts       →  tests/typography/fonts.tests.scss
src/modules/borders/border-radius  →  tests/borders/border-radius.tests.scss
src/modules/layout/grid            →  tests/layout/grid.tests.scss

Import conventions

Always @use sass-true. Two forms exist in the codebase — prefer the first (alias form) for new tests, but be consistent within a file:

// Preferred (alias)
@use 'sass-true' as true;

// Also acceptable (named access)
@use 'sass-true/sass/true';

Import the module under test with a relative path from the test file to src/:

@use '../../src/modules/typography/fonts';
@use '../../src/modules/variables' as vars;

When the module uses a $testing guard (to suppress media queries or side-effecting output during tests), set it before any includes:

vars.$testing: true;

Test structure

Tests follow a strict three-level nesting: describe → it → assert.

@include true.describe('mixin-or-function-name($param1, $param2)') {
  @include true.it('should describe expected behavior') {
    @include true.assert() {
      @include true.output() {
        // Call the mixin/function here
        @include my-module.my-mixin(arg1, arg2);
      }
      @include true.expect() {
        // Paste the exact CSS properties that should be emitted
        property: value;
      }
    }
  }
}

Naming conventions

• describe label: the mixin or function signature — e.g., 'generate($spacing, $divisions)', 'partial-border-radius($top-left, $top-right, $bottom-right, $bottom-left)'
• it label: plain English describing the specific scenario — e.g., 'should set font family and size', 'should throw if spacing is not a number'

Choosing the right assertion

expect — exact match

Use when the mixin emits a known, deterministic set of CSS properties:

@include true.output() {
  @include border.partial-border-radius($top-right: 10px, $bottom-right: 1.2em);
}
@include true.expect() {
  border: {
    top-left-radius: 0;
    top-right-radius: 10px;
    bottom-right-radius: 1.2em;
    bottom-left-radius: 0;
  }
}

contains — partial match

Use when the mixin emits error comments, or when the output also contains unrelated rules you don't want to assert on (e.g., responsive mixins that generate many classes):

@include true.output() {
  @include grid.generate('invalid');
}
@include true.contains() {
  /* ERROR [generate($spacing, $divisions)]: */
  /*   Please provide number parameter! Given value: invalid */
}

Rule of thumb: use expect for normal/happy-path cases, contains for error paths and large output blocks.

Testing error/guard behavior

Sass errors emitted via @error appear as CSS comments in the compiled output. Assert them with contains:

@include true.it('should throw if only one property is defined') {
  @include true.assert() {
    @include true.output() {
      @include fonts.define-font('Arial'); // only family, missing size or weight
    }
    @include true.contains() {
      /* ERROR [define-font($family, $size, $weight)]: */
      /*   At least two of the font properties must be provided. */
    }
  }
}

The error comment format follows the pattern the existing modules use:

/* ERROR [mixin-name($params)]: */
/*   Human-readable reason. */

Testing optional parameters / named arguments

Test all meaningful combinations of optional parameters — defaults, named keyword arguments, and fully-specified calls:

// Default values only
@include true.it('should set border-radius with default values') {
  @include true.assert() {
    @include true.output() { @include border.partial-border-radius(); }
    @include true.expect() { border: { top-left-radius: 0; ... } }
  }
}

// Subset via named args
@include true.it('should set $top-right and $bottom-right') {
  @include true.assert() {
    @include true.output() { @include border.partial-border-radius($top-right: 10px, $bottom-right: 1.2em); }
    @include true.expect() { ... }
  }
}

// All positional args
@include true.it('should set all values') {
  @include true.assert() {
    @include true.output() { @include border.partial-border-radius(4px, 4px, 8px, 8px); }
    @include true.expect() { ... }
  }
}

Testing hover / pseudo-states

When mixins emit nested selectors (e.g., &:hover), write them directly in expect:

@include true.output() {
  @include hover.background-hover(#FFF, #CCC);
}
@include true.expect() {
  background-color: #FFF;

  /* stylelint-disable-next-line nesting-selector-no-missing-scoping-root */
  &:hover, &:hover::before {
    background-color: #CCC;
  }
}

Add / stylelint-disable-next-line nesting-selector-no-missing-scoping-root / before any nested & selector inside expect to suppress stylelint false positives.

Suppressing stylelint in test files

Test files frequently need to suppress rules that are intentional in the context of assertions. Add file-level disables at the top when needed:

/* stylelint-disable scss/no-unused-private-members */
/* stylelint-disable scss/block-no-redundant-nesting */
/* stylelint-disable pitcher/max-lines, plugin/file-max-lines */
/* stylelint-disable shorthand-property-no-redundant-values */
/* stylelint-disable at-rule-allowed-list, number-max-precision */

Only disable what is actually needed for the file.

Coverage checklist when writing tests for a new mixin

1. Happy path with all arguments — verify exact output
2. Happy path with defaults only — verify defaults are applied
3. Happy path with named/keyword arguments — verify partial overrides
4. Error/guard paths — verify error comments are emitted for invalid inputs
5. Edge values — zero, null, wrong type, out-of-range numbers (where the mixin guards against them)