packtpublishing/claude---master-claude-cowork-claude-code-skills-plugins/test-writer

Test Writer

Process

1. Read the source file to understand what it does
2. Identify all functions, methods, and branches to test
3. Check if a test file already exists
4. Write comprehensive tests following the project conventions
5. Run the tests to verify they pass

Test Structure

describe('ModuleName', () => {
  describe('functionName', () => {
    it('should [expected behavior] when [condition]', () => {
      // Arrange
      // Act
      // Assert
    });
  });
});

What to Test

• Happy path: normal inputs produce expected outputs
• Edge cases: empty inputs, null, undefined, zero, max values
• Error cases: invalid inputs throw or return errors
• Boundary conditions: limits, off-by-one scenarios
• Async behavior: promises resolve/reject correctly
• Side effects: external calls are made with correct args

Rules

• Test file goes next to source: file.ts → file.test.ts
• Use descriptive test names that read like sentences
• Each test tests ONE thing
• Use describe blocks to group related tests
• Mock external dependencies (APIs, databases, file system)
• Don't test implementation details — test behavior
• After writing, run npm test to verify all tests pass
• Aim for at least 80% coverage of the target file