What Is Software Testing? A Guide to Test Types

"It works" and "it works correctly" are very different things. Writing tests is tedious — but not writing tests is far more expensive. Fixing a bug in production costs 30 times more than fixing it during development.

Why Write Tests?

• Catches errors early
• Makes refactoring safe
• Serves as documentation
• Prevents regression
• Improves code quality
• Increases deployment confidence

The Testing Pyramid

The testing pyramid shows the layers and proportions of tests:

Unit Tests (Base — most): Tests a single function or component.

Integration Tests (Middle): Tests multiple units working together.

E2E Tests (Top — fewest): Tests the entire application from the user's perspective.

Test Types

1. Unit Test

Tests a single function or component in isolation.

// sum.js
function sum(a, b) {
  return a + b;
}

// sum.test.js
test('adds two numbers', () => {
  expect(sum(2, 3)).toBe(5);
});

test('works with negative numbers', () => {
  expect(sum(-1, -2)).toBe(-3);
});

Tools: Jest, Vitest, Mocha

2. Integration Test

Tests multiple units working together.

test('user registration and login', async () => {
  await request(app)
    .post('/api/register')
    .send({ email: 'test@test.com', password: '12345678' })
    .expect(201);

  const res = await request(app)
    .post('/api/login')
    .send({ email: 'test@test.com', password: '12345678' })
    .expect(200);

  expect(res.body.token).toBeDefined();
});

Tools: Supertest, Testing Library

3. E2E (End-to-End) Test

Tests the entire application from start to finish.

test('user logs in and sees dashboard', async ({ page }) => {
  await page.goto('/login');
  await page.fill('#email', 'test@test.com');
  await page.fill('#password', '12345678');
  await page.click('button[type="submit"]');
  await expect(page).toHaveURL('/dashboard');
  await expect(page.locator('h1')).toContainText('Welcome');
});

Tools: Playwright, Cypress, Selenium

4. Snapshot Test

Checks whether a component's appearance has changed.

5. Performance Test

Tests application behavior under load.

6. Security Test

Scans for security vulnerabilities.

TDD (Test-Driven Development)

Test-first development cycle:

1. Red — Write test first (it fails)
2. Green — Write minimum code to pass
3. Refactor — Improve code (test still passes)

Test Coverage Targets

| Layer | Target | |-------|--------| | Unit tests | 80 percent+ | | Integration tests | Critical flows | | E2E tests | Core user scenarios | | Overall | 70-80 percent |

Testing Tools

| Tool | Type | Language | |------|------|----------| | Jest | Unit/Integration | JavaScript | | Vitest | Unit/Integration | JavaScript (fast) | | Playwright | E2E | Multi-language | | Cypress | E2E | JavaScript | | Testing Library | Component | React/Vue/Angular | | SonarQube | Code quality | Multi-language | | k6 | Performance | JavaScript |

Testing Best Practices

1. AAA pattern — Arrange, Act, Assert
2. Independent tests — Each test runs in isolation
3. Meaningful names — Not "test1", but "user logs in"
4. Mock and stub — Isolate external dependencies
5. Run automatically in CI/CD
6. Test edge cases — Boundary values, empty data

Conclusion

Software testing is an investment — it doesn't directly generate revenue but dramatically reduces the cost of bugs. Start with unit tests, then cover critical flows with integration tests. Teams that write tests release faster and more confidently.

For software testing strategy and automation consulting, get in touch: info@cagribilgehan.com. Check out my projects: cagribilgehan.com