vitest-testing - SKILL.md Agent Skill

name: vitest-testing description: Write and run Vitest unit and integration tests. Use when creating tests, debugging test failures, or checking test coverage. metadata: version: '1.0'

Vitest Testing

Running Tests

# Run all tests
npx vitest run

# Run in watch mode
npx vitest

# Run with coverage
npx vitest run --coverage

# Run a specific test file
npx vitest run src/utils/stats.test.ts

# Run tests matching a pattern
npx vitest run -t "rolling average"

Test File Naming

Unit tests: <module>.test.ts co-located with the source file
Integration tests: <feature>.integration.test.ts in a __tests__/ directory

Test Structure

import { describe, it, expect, beforeEach, vi } from 'vitest';

describe('ModuleName', () => {
  describe('functionName', () => {
    it('should describe expected behavior', () => {
      // Arrange
      const input = createTestInput();

      // Act
      const result = functionName(input);

      // Assert
      expect(result).toEqual(expectedOutput);
    });

    it('should handle edge case', () => {
      expect(() => functionName(null)).toThrow('Expected valid input');
    });
  });
});

Best Practices

Test behavior, not implementation. If internal refactoring breaks tests, the tests are too coupled.
Use descriptive test names: should calculate rolling AHI average with gaps in data
Test edge cases: empty arrays, single elements, NaN values, boundary conditions.
Mock external dependencies (IndexedDB, OPFS, Web Workers) using vi.mock().
Use beforeEach for setup, not shared mutable state.
For statistical functions, compare against known values from reference implementations.
Use toBeCloseTo() for floating-point comparisons.