Testing

Quick Reference

yarn test        # watch mode
yarn test:run    # single run

Test Structure

Test files live alongside source or in a tests/ directory:

• src/lib/ts/tests/ — TypeScript unit tests
• Name pattern: Foo.test.ts

Adding Tests

1. Create Foo.test.ts in your tests directory
2. Import from relative path: import { Foo } from '../path/to/Foo'
3. Import Extensions if needed: import '../common/Extensions'

import { describe, it, expect } from 'vitest';
import { Thing } from '../types/Thing';

describe('Thing', () => {
  it('does something', () => {
    expect(new Thing().value).toBe(42);
  });
});

Common Patterns

Testing Pure Functions

describe('calculateTotal', () => {
  it('sums array of numbers', () => {
    expect(calculateTotal([1, 2, 3])).toBe(6);
  });

  it('returns 0 for empty array', () => {
    expect(calculateTotal([])).toBe(0);
  });
});

Testing Classes

describe('Point', () => {
  it('creates with x and y', () => {
    const p = new Point(10, 20);
    expect(p.x).toBe(10);
    expect(p.y).toBe(20);
  });

  it('calculates distance', () => {
    const p1 = new Point(0, 0);
    const p2 = new Point(3, 4);
    expect(p1.distanceTo(p2)).toBe(5);
  });
});

Testing Edge Cases

describe('Angle', () => {
  it('handles zero correctly', () => {
    // 0 is falsy but valid angle
    expect(cursor_forAngle(0)).toBe('e-resize');
  });

  it('handles boundary values', () => {
    expect(quadrant_forAngle(0)).toBe(1);
    expect(quadrant_forAngle(90)).toBe(2);
    expect(quadrant_forAngle(360)).toBe(1); // wraps
  });
});

What to Test

Good candidates:

• Pure functions (no side effects)
• Geometry/math utilities
• Data transformations
• String/array helpers
• State transitions

Skip for now:

• Canvas/WebGL rendering
• Svelte components (needs @testing-library/svelte)
• Browser APIs
• Async network calls

Config

• vitest.config.ts — test configuration
• Exclude app entry points from test discovery

Debugging Tests

# Run specific test file
yarn test Angle.test.ts

# Run tests matching pattern
yarn test -t "calculates distance"

# Show console output
yarn test --reporter=verbose