What Is Software Testing? Test Types and Best Practices

"We don't have time to write tests." This is one of the most dangerous sentences in a software project. Not writing tests doesn't save time — it borrows future time loss against today.

Why Write Tests?

• Confidence — Know nothing is broken when you change code
• Documentation — Tests document how code should behave
• Refactoring safety — Restructure code safely with tests in place
• Fewer bugs — Catch errors before production
• Speed — Long-term development velocity increases

The Test Pyramid

Mike Cohn's test pyramid shows the ideal distribution of tests:

        ╱╲
       ╱  ╲       E2E Tests (few, slow, expensive)
      ╱────╲
     ╱      ╲     Integration Tests (moderate)
    ╱────────╲
   ╱          ╲   Unit Tests (many, fast, cheap)
  ╱────────────╲

Unit Tests

Test the smallest code units (functions, methods) in isolation:

function calculateDiscount(price: number, isPremium: boolean): number {
  if (isPremium) return price * 0.2;
  if (price > 100) return price * 0.1;
  return 0;
}

describe('calculateDiscount', () => {
  it('should apply 20% for premium users', () => {
    expect(calculateDiscount(500, true)).toBe(100);
  });
  it('should apply 10% for orders over $100', () => {
    expect(calculateDiscount(150, false)).toBe(15);
  });
  it('should not discount normal orders', () => {
    expect(calculateDiscount(50, false)).toBe(0);
  });
});

Integration Tests

Test how multiple units work together:

describe('Order Flow', () => {
  it('should decrease stock when order is created', async () => {
    const product = await createProduct({ stock: 10 });
    await createOrder({ productId: product.id, quantity: 3 });
    const updated = await getProduct(product.id);
    expect(updated.stock).toBe(7);
  });
});

E2E Tests

Test the application from the user's perspective:

describe('Login Flow', () => {
  it('should login with valid credentials', () => {
    cy.visit('/login');
    cy.get('#email').type('test@example.com');
    cy.get('#password').type('password123');
    cy.get('#login-btn').click();
    cy.url().should('include', '/dashboard');
    cy.contains('Welcome').should('be.visible');
  });
});

Testing Tools

| Tool | Language/Platform | Type | |------|------------------|------| | Jest | JavaScript/TypeScript | Unit, Integration | | Vitest | Vite-based projects | Unit, Integration | | Cypress | Web | E2E | | Playwright | Web | E2E | | pytest | Python | Unit, Integration | | JUnit | Java | Unit |

Test-Driven Development (TDD)

Write the test first, then the code:

1. 🔴 Red    — Write a failing test
2. 🟢 Green  — Write minimum code to pass
3. 🔵 Refactor — Clean up, test still passes
4. Repeat

Best Practices

AAA Pattern

Arrange — Set up (prepare test data)
Act     — Execute (run the tested code)
Assert  — Verify (check the result)

F.I.R.S.T

• Fast — Tests should run quickly
• Independent — Tests should not depend on each other
• Repeatable — Same result every time
• Self-validating — Automatic pass/fail
• Timely — Written alongside the code

Conclusion

Writing tests is not a cost, it's an investment. It takes time initially, but returns tenfold over the project's lifetime. Start by testing critical business logic and frequently changing code.

Learn testing practices with interactive missions at LabLudus.