refactor: extracted code examples

[mfranzke]

Description

As code examples for transformations of input CSS to output CSS are spread through the whole codebase in tests and documentation, we should ensure somehow to reduce redundancies as well as having a single source of truth to correct some code in case of any mistakes or necessary updates.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Performance improvement
• Code refactoring

Testing

• Tests pass locally
• Added tests for new functionality
• Updated existing tests
• Manual testing completed

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published

Browser Testing

If applicable, please test in the following browsers:

• Chrome
• Firefox
• Safari
• Edge

Performance Impact

If this change affects performance:

• I have run performance benchmarks
• Performance impact is documented
• Performance regression is acceptable for the added functionality

Breaking Changes

If this introduces breaking changes, please describe:

Additional Notes

Any additional information that reviewers should know.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 43235e0

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[Copilot]

Pull Request Overview

This PR refactors CSS test data by extracting inline code examples from test files into a centralized fixture system. This establishes a single source of truth for CSS transformation examples, reducing duplication and improving maintainability across the codebase.

• Creates centralized test fixtures in test/fixtures/ with input/expected pairs
• Implements fixture utilities for loading test data programmatically
• Adds automated documentation generation that syncs fixture data with README examples

Reviewed Changes

Copilot reviewed 28 out of 28 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
test/fixtures/*.css	New centralized CSS test fixtures with input/expected pairs
test/fixture-utils.js	Utility functions for loading and managing test fixtures
scripts/build-docs.js	Automated documentation builder that injects fixture examples
packages/postcss-if-function/test/plugin.test.js	Refactored to use centralized fixtures instead of inline CSS
packages/css-if-polyfill/test/integrated.test.js	Updated to load fixtures for integration tests
packages/postcss-if-function/README.md	Updated with auto-generated fixture examples
package.json	Added build:docs script for documentation generation
docs/*.md	New documentation files demonstrating the fixture system

[github-actions]

🚀 Performance Benchmark Results

Metric	Value	Status
Initialization Time	0.50ms	✅
Avg Processing Time	0.2394ms	✅
Total Processing Time (1000x)	239.40ms	ℹ️

✅ All benchmarks passed!

[github-actions]

🚀 Performance Benchmark Results

Metric	Value	Status
Initialization Time	0.50ms	✅
Avg Processing Time	0.2660ms	✅
Total Processing Time (1000x)	266.00ms	ℹ️

✅ All benchmarks passed!