arosenkranz/automating-tests

Test Automation

Build comprehensive test suites following the test pyramid pattern.

Test Pyramid

     /\
    /E2E\      <- Few, slow, expensive
   /------\
  / INTEG  \   <- Some, medium speed
 /----------\
/   UNIT     \ <- Many, fast, cheap
--------------

Focus: Many unit tests, fewer integration tests, minimal E2E tests.

Unit Tests

Test Structure (Arrange-Act-Assert)

// Jest example
describe('UserService', () => {
  describe('createUser', () => {
    it('creates user with valid data', async () => {
      // Arrange
      const service = new UserService();
      const userData = {
        email: '[email protected]',
        name: 'Test User'
      };

      // Act
      const user = await service.createUser(userData);

      // Assert
      expect(user).toMatchObject(userData);
      expect(user.id).toBeDefined();
      expect(user.createdAt).toBeInstanceOf(Date);
    });

    it('throws ValidationError for invalid email', async () => {
      // Arrange
      const service = new UserService();

      // Act & Assert
      await expect(
        service.createUser({ email: 'invalid', name: 'Test' })
      ).rejects.toThrow(ValidationError);
    });
  });
});

pytest Example

import pytest
from user_service import UserService, ValidationError

class TestUserService:
    @pytest.fixture
    def service(self):
        """Provide fresh UserService for each test."""
        return UserService()

    def test_create_user_with_valid_data(self, service):
        # Arrange
        user_data = {
            'email': '[email protected]',
            'name': 'Test User'
        }

        # Act
        user = service.create_user(user_data)

        # Assert
        assert user.email == user_data['email']
        assert user.name == user_data['name']
        assert user.id is not None

    def test_create_user_invalid_email(self, service):
        # Act & Assert
        with pytest.raises(ValidationError, match="Invalid email"):
            service.create_user({'email': 'invalid', 'name': 'Test'})

    @pytest.mark.parametrize('email,should_pass', [
        ('[email protected]', True),
        ('[email protected]', True),
        ('invalid', False),
        ('@example.com', False),
        ('user@', False),
    ])
    def test_email_validation(self, service, email, should_pass):
        if should_pass:
            user = service.create_user({'email': email, 'name': 'Test'})
            assert user.email == email
        else:
            with pytest.raises(ValidationError):
                service.create_user({'email': email, 'name': 'Test'})

Mocking and Stubbing

Jest Mocks

import { fetchUserData } from './api';
import { processUser } from './user-processor';

jest.mock('./api');

describe('processUser', () => {
  it('processes user data from API', async () => {
    // Mock the API call
    fetchUserData.mockResolvedValue({
      id: 1,
      name: 'John',
      email: '[email protected]'
    });

    const result = await processUser(1);

    expect(fetchUserData).toHaveBeenCalledWith(1);
    expect(result.name).toBe('JOHN'); // uppercase transformation
  });

  it('handles API errors', async () => {
    fetchUserData.mockRejectedValue(new Error('API failed'));

    await expect(processUser(1)).rejects.toThrow('API failed');
  });
});

pytest Mocking

from unittest.mock import Mock, patch, MagicMock
import pytest

def test_user_processor_with_mock(mocker):
    # Using pytest-mock
    mock_api = mocker.patch('module.fetch_user_data')
    mock_api.return_value = {
        'id': 1,
        'name': 'John',
        'email': '[email protected]'
    }

    result = process_user(1)

    mock_api.assert_called_once_with(1)
    assert result['name'] == 'JOHN'

def test_database_interaction():
    # Mock database connection
    mock_db = Mock()
    mock_db.query.return_value = [{'id': 1, 'name': 'Test'}]

    service = UserService(db=mock_db)
    users = service.get_all_users()

    mock_db.query.assert_called_once()
    assert len(users) == 1

Fixtures and Test Data

pytest Fixtures

import pytest
from database import Database

@pytest.fixture(scope='session')
def database():
    """Session-wide database connection."""
    db = Database(':memory:')
    db.create_tables()
    yield db
    db.close()

@pytest.fixture
def sample_users():
    """Provide sample user data."""
    return [
        {'email': '[email protected]', 'name': 'User 1'},
        {'email': '[email protected]', 'name': 'User 2'},
    ]

@pytest.fixture
def user_service(database):
    """Provide UserService with test database."""
    return UserService(database)

def test_bulk_create(user_service, sample_users):
    created = user_service.bulk_create(sample_users)
    assert len(created) == 2

Jest Setup/Teardown

describe('DatabaseTests', () => {
  let db;

  beforeAll(async () => {
    // Run once before all tests
    db = await Database.connect(':memory:');
    await db.createTables();
  });

  afterAll(async () => {
    // Run once after all tests
    await db.close();
  });

  beforeEach(async () => {
    // Run before each test
    await db.clearTables();
  });

  it('inserts user', async () => {
    await db.insert('users', { name: 'Test' });
    const users = await db.query('users');
    expect(users).toHaveLength(1);
  });
});

Integration Tests

Test with Real Dependencies

import pytest
from testcontainers.postgres import PostgresContainer

@pytest.fixture(scope='module')
def postgres_container():
    """Provide PostgreSQL container for integration tests."""
    with PostgresContainer('postgres:15') as postgres:
        yield postgres

@pytest.fixture
def db_connection(postgres_container):
    """Provide database connection."""
    conn = create_connection(postgres_container.get_connection_url())
    setup_schema(conn)
    yield conn
    conn.close()

def test_user_repository_integration(db_connection):
    repo = UserRepository(db_connection)

    # Insert user
    user = repo.create({'email': '[email protected]', 'name': 'Test'})
    assert user.id is not None

    # Retrieve user
    retrieved = repo.get_by_id(user.id)
    assert retrieved.email == '[email protected]'

    # Update user
    repo.update(user.id, {'name': 'Updated'})
    updated = repo.get_by_id(user.id)
    assert updated.name == 'Updated'

API Integration Tests

import request from 'supertest';
import app from './app';

describe('API Integration Tests', () => {
  it('creates and retrieves user', async () => {
    // Create user
    const createResponse = await request(app)
      .post('/api/users')
      .send({ email: '[email protected]', name: 'Test' })
      .expect(201);

    const userId = createResponse.body.id;

    // Retrieve user
    const getResponse = await request(app)
      .get(`/api/users/${userId}`)
      .expect(200);

    expect(getResponse.body.email).toBe('[email protected]');
  });

  it('returns 404 for non-existent user', async () => {
    await request(app)
      .get('/api/users/999')
      .expect(404);
  });
});

End-to-End Tests

Playwright Example

import { test, expect } from '@playwright/test';

test.describe('User Registration', () => {
  test('completes registration flow', async ({ page }) => {
    // Navigate to registration page
    await page.goto('/register');

    // Fill form
    await page.fill('[data-testid="email-input"]', '[email protected]');
    await page.fill('[data-testid="password-input"]', 'SecurePass123');
    await page.fill('[data-testid="name-input"]', 'Test User');

    // Submit form
    await page.click('[data-testid="submit-button"]');

    // Wait for redirect
    await page.waitForURL('/dashboard');

    // Verify success
    await expect(page.locator('[data-testid="welcome-message"]'))
      .toContainText('Welcome, Test User');
  });

  test('shows validation errors', async ({ page }) => {
    await page.goto('/register');

    // Submit without filling
    await page.click('[data-testid="submit-button"]');

    // Check error messages
    await expect(page.locator('[data-testid="email-error"]'))
      .toContainText('Email is required');
  });
});

Cypress Example

describe('User Dashboard', () => {
  beforeEach(() => {
    // Login before each test
    cy.login('[email protected]', 'password');
    cy.visit('/dashboard');
  });

  it('displays user information', () => {
    cy.get('[data-cy=user-name]').should('contain', 'Test User');
    cy.get('[data-cy=user-email]').should('contain', '[email protected]');
  });

  it('updates profile', () => {
    cy.get('[data-cy=edit-profile]').click();
    cy.get('[data-cy=name-input]').clear().type('Updated Name');
    cy.get('[data-cy=save-button]').click();

    cy.get('[data-cy=success-message]')
      .should('be.visible')
      .and('contain', 'Profile updated');
  });
});

CI/CD Integration

GitHub Actions

name: Test

on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest

    services:
      postgres:
        image: postgres:15
        env:
          POSTGRES_PASSWORD: postgres
        options: >-
          --health-cmd pg_isready
          --health-interval 10s
          --health-timeout 5s
          --health-retries 5

    steps:
      - uses: actions/checkout@v4

      - name: Setup Node.js
        uses: actions/setup-node@v4
        with:
          node-version: '18'
          cache: 'npm'

      - name: Install dependencies
        run: npm ci

      - name: Run unit tests
        run: npm run test:unit

      - name: Run integration tests
        run: npm run test:integration
        env:
          DATABASE_URL: postgres://postgres:postgres@localhost:5432/test

      - name: Run E2E tests
        run: npm run test:e2e

      - name: Upload coverage
        uses: codecov/codecov-action@v3
        with:
          files: ./coverage/lcov.info

Coverage Analysis

Jest Coverage

# Run with coverage
npm test -- --coverage

# Coverage thresholds in package.json
{
  "jest": {
    "coverageThreshold": {
      "global": {
        "branches": 80,
        "functions": 80,
        "lines": 80,
        "statements": 80
      }
    }
  }
}

pytest Coverage

# Run with coverage
pytest --cov=src --cov-report=html --cov-report=term

# Config in .coveragerc
[run]
source = src
omit = */tests/*

[report]
fail_under = 80

Best Practices

1. Test behavior, not implementation
2. One assertion concept per test
3. Make tests independent (no shared state)
4. Use descriptive test names
5. Keep tests fast (parallelize when possible)
6. Mock external dependencies (APIs, databases in unit tests)
7. Test edge cases and error paths
8. Avoid test duplication
9. Clean up resources (use fixtures/teardown)
10. Keep tests maintainable (DRY principle applies)