BEHAVIORAL TESTING IN REACT & REDUX RE-EXAMINING THE UNIT TEST 

WHAT DO WE WANT OUT OF OUR TESTS? ▸ Confidence ▸ The application works as expected ▸ Refactor without changing functionality or tests
 ▸ Documentation ▸ Use the language of the business ▸ Demonstrate conformance to business objectives (user flows, journeys)
 ▸ Act like an application ▸ Run fast ▸ Easy to maintain 

LET’S TALK ABOUT OBJECT-ORIENTED UNIT TESTING 

public class OrderService { public Order open(OrderData newOrderData) { } public boolean submit(String orderId) { } private boolean validate(Order order) { } } 

Object-oriented design treats the class as the unit.
 The methods are the surface area. CLASS AS THE UNIT 

CLASS AS THE UNIT TREE OF CONTRACTS = HIGH SURFACE AREA Orders Controller Products Controller Order Service Product Service Product Order Product View Order View 

CLASS AS THE UNIT ORGANIZE BY LAYER 

CLASS AS THE UNIT WHAT HAPPENS WHEN WE TEST LIKE THIS? ▸ Establish contracts between classes. ▸ Internal refactoring is easy. Surface area refactoring can quickly have ripple effects. ▸ Tests run very fast if providing test doubles for expensive dependencies. ▸ Balance speed vs coverage. ▸ Need wider tests to cover the interaction patterns of multiple classes. 

LET’S TALK ABOUT REACT & REDUX 

REACT REDUX FLUX/REDUX ARCHITECTURE COMPONENTS REDUCERS STORE dispatch actions provides state to 

REACT REDUX FLUX/REDUX ARCHITECTURE VIEW AS A FUNCTION OF STATE FUNCTION STATE VIEW REACT DOM 

REDUX FLUX/REDUX ARCHITECTURE VIEW AS A FUNCTION OF STATE STATE ‣100% of application state stored in the Redux store ‣State always comes from 1 location 

REACT FLUX/REDUX ARCHITECTURE VIEW AS A FUNCTION OF STATE FUNCTION ‣ Components are deterministic, stateless, predictable ‣ Components only have a contract with the Redux state 

FLUX/REDUX ARCHITECTURE VIEW AS A FUNCTION OF STATE VIEW REACT DOM ‣The View is a representation of the UI ‣React DOM is a trusted third party 

// CartComponent.jsx class Cart extends React.Component { componentDidMount() { } handleClick() { } render() { } } export default Cart 

// CartContainer.js function mapStateToProps(state) { } function mapDispatchToProps(dispatch) { } export default connect( mapStateToProps, mapDispatchToProps )(Cart) 

// cartReducer.js function addToCartAction(data) { } function cartReducer(state, action) { } export default cartReducer 

Object-oriented design treats the class as the unit.
 The methods are the surface area. CLASS AS THE UNIT 

React/Redux design treats the function as the unit.
 The functions are the surface area. FUNCTION AS THE UNIT 

// CartComponent.jsx class Cart extends React.Component { componentDidMount() { } _handleClick() { } render() { } } export default Cart // cartReducer.js function addToCartAction(data) { } function cartReducer(state, action) { } export default cartReducer // CartContainer.js function mapStateToProps(state) { } function mapDispatchToProps(dispatch) { } export default connect( mapStateToProps, mapDispatchToProps )(Cart) 

// cartActions.spec.jsx describe('Cart Action Creators', () => { it('creates an add to cart action', () => { const action = addToCartAction('a product name') expect(action).toEqual({ type: 'ADD_TO_CART', productName: 'a product name' }) }) }) // Cart.spec.jsx describe('Cart Component', () => { it('handles the click of the checkout button', () => { const cart = shallow( ).instance() cart.handleClick() expect(mockDispatch).toHaveBeenCalledWith(stubAddToCart) }) }) 

FUNCTION AS THE UNIT WHAT HAPPENS WHEN WE TEST LIKE THIS? ▸ Small refactoring can produce false positives in tests. ▸ A lot of low value tests that must change often. ▸ Encourages unnecessary mocking of inexpensive, deterministic dependencies (Redux store) ▸ Tests don’t reflect business language or objectives. ▸ Need wider tests to cover interaction of component with its own container, actions, and reducer 

Redux has changed how we think about single page apps,
 
 now we need to rethink testing. RE-EXAMINE THE UNIT 

The unit is based on your understanding of the system and its testing.
 The view is the surface area. RE-EXAMINE THE UNIT 

REACT REDUX OUR UNDERSTANDING OF THE SYSTEM VIEW AS A FUNCTION OF STATE FUNCTION STATE VIEW REACT DOM 

VIEW AS THE UNIT 1-WAY CONTRACT = LOW SURFACE AREA Cart ProductPrice BuyButton OrderConfirmation STATE 

VIEW AS THE UNIT ORGANIZE BY COMPONENT 

VIEW AS THE UNIT BEHAVIORAL COMPONENT TEST // Cart.spec.jsx describe('Cart', () => { it('requires login before checking out’, { dispatch( addToCartAction('iPhone 8') ) const cart = shallow() cart.find('#checkout').simulate('click') expect(cart).toHaveText('You must login first.') }) }) 

VIEW AS THE UNIT WHAT HAPPENS WHEN WE TEST LIKE THIS? ▸ Refactor confidently without changing tests. ▸ Test not opinionated about contents of Redux store, action shapes, or the names of props. ▸ More realistic tests without the need for mocks ▸ Better documentation of the business language and user flows ▸ Write fewer tests. Less code to maintain. 

VIEW AS THE UNIT WHAT ENABLES THIS KIND OF TESTING? ▸ Trust in the system and third parties ▸ Strict adherence to React & Redux principles ▸ Most components are connected directly to state ▸ Rarely pass props to children ▸ Most components to not hold local state (no setState) ▸ Enzyme and jsdom unlock fast access to the view 

SUBCUTANEOUS FUNCTIONAL TEST describe('Checkout', () => { jest.mock('../httpClient', stubHttpClient) it("allows a purchase after logging in", async () => { expect.assertions(1); const app = mount() fillIn(app, '#search', 'iPhone 8') await httpReturns({name: 'iPhone 8', price: 899.99}) click(app, '#addToCart') click(app, '#checkout') fillIn(app, '#username', 'jane_doe') await httpReturns({success: true}) expect(app).toHaveText('Thanks for your purchase, Jane!') }) }) 

THEMES ▸ The unit tests in a system are dependent on the paradigms and architecture of that system.
 ▸ Test observable behavior in the UI, not function return values. ▸ Save your mocks for the expensive things. ▸ Focus on enabling safe refactoring without being forced to change tests or wonder if things are working. 

Thanks! Ryan Oglesby
 [email protected]
 @ryanoglesby08