Test Driven Development

# Good: Focused test
def test_should_validate_email_format():
    assert is_valid_email("user@example.com") is True

# Avoid: Multiple unrelated assertions
def test_validation():
    assert is_valid_email("user@example.com") is True
    assert is_valid_phone("123-456-7890") is True  # Different concept

# Good: Each test is self-contained
def test_user_creation():
    user = create_user("test@example.com")
    assert user.email == "test@example.com"

# Avoid: Tests depending on execution order
shared_user = None

def test_create_user():
    global shared_user
    shared_user = create_user("test@example.com")

def test_update_user():  # Depends on previous test
    shared_user.name = "Updated"

# Good: Clear failure message
assert result.status == 200, f"Expected 200, got {result.status}: {result.body}"

# Avoid: Unclear failure
assert result.status == 200

# Good: Reusable test data creation
def create_test_user(**overrides):
    defaults = {
        'email': 'test@example.com',
        'name': 'Test User',
        'role': 'user'
    }
    return User(**{**defaults, **overrides})

# Usage
admin = create_test_user(role='admin')
guest = create_test_user(email='guest@example.com')

# Bad: Tests internal structure
def test_user_storage():
    user = User("test@example.com")
    assert user._internal_cache is not None  # Implementation detail

# Bad: Breaks with harmless changes
assert user.to_json() == '{"name":"John","email":"john@example.com"}'

# Good: Tests behavior, not format
data = json.loads(user.to_json())
assert data['name'] == "John"
assert data['email'] == "john@example.com"

# Bad: Real HTTP calls in unit tests
def test_api_integration():
    response = requests.get("https://api.example.com/users")  # Slow!
    assert response.status_code == 200

# Bad: Testing business logic through UI
def test_calculation():
    browser.click("#input1")
    browser.type("5")
    browser.click("#input2")
    browser.type("3")
    browser.click("#calculate")
    assert browser.find("#result").text == "8"

# Good: Test logic directly
def test_calculation():
    assert calculate(5, 3) == 8

# Setup/Teardown
@pytest.fixture
def database():
    db = create_test_database()
    yield db
    db.cleanup()

# Parametrized tests
@pytest.mark.parametrize("input,expected", [
    ("user@example.com", True),
    ("invalid-email", False),
])
def test_email_validation(input, expected):
    assert is_valid_email(input) == expected

// Setup/Teardown
beforeEach(() => {
  database = createTestDatabase();
});

afterEach(() => {
  database.cleanup();
});

// Async tests
test('should fetch user data', async () => {
  const user = await fetchUser(1);
  expect(user.name).toBe('John');
});

// Table-driven tests
func TestEmailValidation(t *testing.T) {
    tests := []struct {
        input    string
        expected bool
    }{
        {"user@example.com", true},
        {"invalid-email", false},
    }

    for _, tt := range tests {
        result := IsValidEmail(tt.input)
        if result != tt.expected {
            t.Errorf("IsValidEmail(%s) = %v, want %v",
                tt.input, result, tt.expected)
        }
    }
}