Test Pattern Library

Test Pattern Library

Purpose

Provide battle-tested patterns for:

• Unit testing (functions, classes, modules)
• Integration testing (APIs, databases, services)
• End-to-end testing (user workflows)
• Test organization and structure
• Mocking and stubbing strategies
• Test data management

When to Use

Invoke this skill when:

• Writing tests for new code
• Improving test coverage
• Refactoring existing tests
• Teaching testing best practices
• Setting up testing infrastructure
• Debugging flaky tests

Instructions

Step 1: Identify Test Type

Determine what needs testing:

1. Unit Test: Single function/method/class
2. Integration Test: Multiple components working together
3. E2E Test: Complete user workflow
4. Snapshot Test: UI/output comparison
5. Performance Test: Speed/load testing

Step 2: Choose Testing Framework

Select the appropriate framework:

• JavaScript/TypeScript: Jest, Vitest, Mocha, Jasmine
• Python: pytest, unittest
• Go: testing package
• Rust: built-in test framework
• Java: JUnit, TestNG

Step 3: Apply AAA Pattern

Structure tests with:

1. Arrange: Set up test data and dependencies
2. Act: Execute the code being tested
3. Assert: Verify expected outcomes

Step 4: Include Edge Cases

Test for:

• Happy path (normal operation)
• Edge cases (boundary conditions)
• Error conditions (failures, exceptions)
• Null/undefined/empty values
• Invalid inputs

Testing Patterns

JavaScript/TypeScript (Jest/Vitest)

Unit Test Pattern

import { ${functionName} } from './${moduleName}';

describe('${functionName}', () => {
  // Happy path
  it('should ${expectedBehavior} when given valid input', () => {
    // Arrange
    const input = ${validInput};
    const expected = ${expectedOutput};

    // Act
    const result = ${functionName}(input);

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

  // Edge cases
  it('should handle empty input', () => {
    const result = ${functionName}('');
    expect(result).toBe(${emptyResult});
  });

  it('should handle null input', () => {
    const result = ${functionName}(null);
    expect(result).toBeNull();
  });

  // Error conditions
  it('should throw error for invalid input', () => {
    expect(() => ${functionName}(${invalidInput}))
      .toThrow('${expectedErrorMessage}');
  });
});