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Testing Guide

Testing best practices for Python, JavaScript, and shell scripts.

In This Section

Document Description
Python Testing pytest and testing Python code
JavaScript Testing Vitest, Jest, and frontend testing
Bash Testing Testing shell scripts

Testing Philosophy

The Testing Pyramid

        /\
       /  \
      / E2E\        Few, slow, expensive
     /──────\
    / Integr-\      Some, medium speed
   /  ation   \
  /────────────\
 /    Unit      \   Many, fast, cheap
/________________\

When to Write Tests

  • Unit tests: Pure functions, business logic
  • Integration tests: API endpoints, database operations
  • E2E tests: Critical user flows

What Not to Test

  • Third-party libraries
  • Trivial code (getters, setters)
  • Private implementation details
  • Generated code

Quick Start

Python (pytest)

# Install
pip install pytest pytest-cov

# Run tests
pytest

# With coverage
pytest --cov=src

# test_example.py
def test_addition():
    assert 1 + 1 == 2

JavaScript (Vitest)

# Install
npm install -D vitest

# Run tests
npx vitest

// example.test.js
import { describe, it, expect } from 'vitest'

describe('math', () => {
  it('adds numbers', () => {
    expect(1 + 1).toBe(2)
  })
})

Bash (Bats)

# Install
npm install -g bats

# Run tests
bats tests/

# test_example.bats
@test "echo works" {
  result="$(echo hello)"
  [ "$result" = "hello" ]
}

Test Structure

Arrange-Act-Assert

def test_user_creation():
    # Arrange
    name = "Alice"
    email = "alice@example.com"

    # Act
    user = create_user(name, email)

    # Assert
    assert user.name == name
    assert user.email == email

Given-When-Then (BDD)

def test_user_login():
    # Given a registered user
    user = create_user("alice", "password123")

    # When they attempt to login with correct credentials
    result = login("alice", "password123")

    # Then they should be authenticated
    assert result.authenticated is True

Naming Conventions

Test Files

Python:  test_module.py or module_test.py
JS:      module.test.js or module.spec.js
Bash:    test_script.bats

Test Functions

# Good - descriptive
def test_user_with_invalid_email_raises_error():
    ...

def test_calculate_discount_with_coupon_code():
    ...

# Bad - vague
def test_user():
    ...

def test_calculate():
    ...

Fixtures and Mocking

Python Fixtures

import pytest

@pytest.fixture
def sample_user():
    return User(name="Test", email="test@example.com")

def test_user_greeting(sample_user):
    assert sample_user.greet() == "Hello, Test!"

JavaScript Mocks

import { vi, describe, it, expect } from 'vitest'

const mockFetch = vi.fn()
global.fetch = mockFetch

describe('API', () => {
  it('fetches data', async () => {
    mockFetch.mockResolvedValueOnce({
      json: () => Promise.resolve({ data: 'test' })
    })

    const result = await fetchData()
    expect(result.data).toBe('test')
  })
})

CI Integration

GitHub Actions

# .github/workflows/test.yml
name: Test

on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      - name: Set up Python
        uses: actions/setup-python@v5
        with:
          python-version: '3.12'

      - name: Install dependencies
        run: pip install -e ".[dev]"

      - name: Run tests
        run: pytest --cov --cov-report=xml

      - name: Upload coverage
        uses: codecov/codecov-action@v4

See Also