Writing tests for new code
Improving test coverage
Establishing testing standards
Refactoring with test safety
Implementing TDD (Test-Driven Development)
Creating test utilities and mocks

Quick Start

Minimal working example:

// Jest/JavaScript example
describe("UserService", () => {
  describe("createUser", () => {
    it("should create user with valid data", async () => {
      // Arrange - Set up test data and dependencies
      const userData = {
        email: "john@example.com",
        firstName: "John",
        lastName: "Doe",
      };
      const mockDatabase = createMockDatabase();
      const service = new UserService(mockDatabase);

      // Act - Execute the function being tested
      const result = await service.createUser(userData);

      // Assert - Verify the outcome
      expect(result.id).toBeDefined();
      expect(result.email).toBe("john@example.com");
      expect(mockDatabase.save).toHaveBeenCalledWith(
        expect.objectContaining(userData),
      );
    });
  });
});

Reference Guides

Detailed implementations in the references/ directory:

Guide	Contents
Test Structure (AAA Pattern)	Test Structure (AAA Pattern)
Test Cases by Language	Test Cases by Language
Mocking & Test Doubles	Mocking & Test Doubles
Testing Async Code	Testing Async Code, Test Coverage
Testing Edge Cases	Testing Edge Cases
Example: Complete Test Suite	import { UserService } from "./user-service";

Best Practices

✅ DO

Write tests before or alongside code (TDD)
Test one thing per test
Use descriptive test names
Follow AAA pattern
Test edge cases and error conditions
Keep tests isolated and independent
Use setup/teardown appropriately
Mock external dependencies
Aim for high coverage on critical paths
Make tests fast (< 10ms each)
Use parameterized tests for similar cases
Test public interfaces, not implementation

❌ DON'T

Test implementation details
Write tests that depend on each other
Ignore failing tests
Test third-party library code
Use real databases/APIs in unit tests
Make tests too complex
Skip edge cases
Forget to clean up resources
Test everything (focus on business logic)
Write flaky tests

unit-testing-framework

Unit Testing Framework

Table of Contents

Overview

When to Use