test-generator

Test Generator

When to use this skill

• Adding test coverage to existing code
• Writing tests for a new feature
• Generating edge case tests
• Setting up a test suite from scratch
• Improving test quality or coverage

Step 1: Understand the testing environment

Before writing tests, identify the project's test setup:

# Check for test config files
ls jest.config* vitest.config* pytest.ini setup.cfg pyproject.toml .mocharc* 2>/dev/null

# Check package.json test scripts
grep -A 5 '"test"' package.json

# Find existing test files for patterns
find . -name "*.test.*" -o -name "*.spec.*" -o -name "test_*" | head -20

Step 2: Read the source code

Read the code you're testing thoroughly:

• Inputs: What parameters does the function accept?
• Outputs: What does it return or produce?
• Side effects: Does it write to DB, call APIs, modify state?
• Error paths: When does it throw or return errors?
• Edge cases: Empty inputs, null, boundaries, concurrency

Step 3: Write tests following existing patterns

Test structure (Arrange-Act-Assert)

// TypeScript/Jest/Vitest
describe('calculateDiscount', () => {
  it('should apply percentage discount to total', () => {
    // Arrange
    const items = [{ price: 100 }, { price: 50 }];
    const discountPercent = 10;

    // Act
    const result = calculateDiscount(items, discountPercent);

    // Assert
    expect(result).toBe(135);
  });

  it('should return original total when discount is 0', () => {
    const items = [{ price: 100 }];
    expect(calculateDiscount(items, 0)).toBe(100);
  });

  it('should throw when discount exceeds 100%', () => {
    expect(() => calculateDiscount([{ price: 100 }], 150))
      .toThrow('Discount cannot exceed 100%');
  });
});

# Python/pytest
class TestCalculateDiscount:
    def test_applies_percentage_discount(self):
        items = [{"price": 100}, {"price": 50}]
        assert calculate_discount(items, 10) == 135

    def test_zero_discount_returns_original(self):
        items = [{"price": 100}]
        assert calculate_discount(items, 0) == 100

    def test_raises_on_excessive_discount(self):
        with pytest.raises(ValueError, match="cannot exceed 100%"):
            calculate_discount([{"price": 100}], 150)