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JazzCon 2018: Effective React Testing
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Jeremy Fairbank
March 22, 2018
Programming
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JazzCon 2018: Effective React Testing
Jeremy Fairbank
March 22, 2018
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Transcript
Effective React Testing Jeremy Fairbank @elpapapollo
@testdouble helps improves how the world build software. testdouble.com/agency
In beta now! bit.ly/programming-elm
My shiny new React application…
…without tests.
None
None
API Design
Refactoring
?
redux-thunk +
Components Test expected output.
Reducer Test state changes as expected.
Actions Test actions through reducer tests. Test thunks for coordination.
E2E Integration Unit Snapshot $$$ $
E2E Integration Unit Snapshot $$$ $
E2E Integration Unit Snapshot $$$ $
E2E Integration Unit Snapshot $$$ $
E2E Integration Unit Snapshot $$$ $
None
Jest facebook.github.io/jest
1. Automatic with create-react-app 2. Or add yourself: yarn add
jest npm install --save jest
Enzyme JavaScript testing utilities for React. github.com/airbnb/enzyme yarn add enzyme
enzyme-adapter-react-16
TDD with Components <NameTag name="Jeremy" employer="Test Double" /> expect "Hello.
I'm Jeremy from Test Double."
DEMO
Unit Tests Recap
Unit Tests Recap
Unit Tests Recap Easy to write
Unit Tests Recap Easy to write Fast
Unit Tests Recap Easy to write Fast Isolated design feedback
Unit Tests Recap Easy to write Fast Isolated design feedback
Unit Tests Recap Easy to write Fast Isolated design feedback
Tedious to test all components
Unit Tests Recap Easy to write Fast Isolated design feedback
Tedious to test all components Coupled to implementation
Unit Tests Recap Easy to write Fast Isolated design feedback
Tedious to test all components Coupled to implementation No interaction with other components
Snapshot Tests Recap
Snapshot Tests Recap
Snapshot Tests Recap Easily test component tree
Snapshot Tests Recap Easily test component tree Fast
Snapshot Tests Recap Easily test component tree Fast Fill in
test gaps quickly
Snapshot Tests Recap Easily test component tree Fast Fill in
test gaps quickly Regression safety
Snapshot Tests Recap Easily test component tree Fast Fill in
test gaps quickly Regression safety
Snapshot Tests Recap Easily test component tree Fast Fill in
test gaps quickly Regression safety No design feedback
Snapshot Tests Recap Easily test component tree Fast Fill in
test gaps quickly Regression safety No design feedback Break from markup changes
Snapshot Tests Recap Easily test component tree Fast Fill in
test gaps quickly Regression safety No design feedback Break from markup changes Prone to human error
Integration Tests Recap
Integration Tests Recap ⚙⚙
Integration Tests Recap ⚙ Test component’s interaction with child components
⚙
Integration Tests Recap ⚙ Test component’s interaction with child components
⚙
Integration Tests Recap ⚙ Test component’s interaction with child components
Coupled to child component implementation ⚙
Integration Tests Recap ⚙ Test component’s interaction with child components
Coupled to child component implementation Redundant test coverage ⚙
Integration Tests Recap ⚙ Test component’s interaction with child components
Coupled to child component implementation Redundant test coverage Harder to debug ⚙
E2E Integration Unit Snapshot $$$ $
E2E Integration Unit Snapshot $$$ $
Reducer Action New State State Testing Redux
DEMO
Unit Tests “Redux”
Unit Tests “Redux”
Unit Tests “Redux” Easier to write Fast Isolated design feedback
Unit Tests “Redux” Easier to write Fast Isolated design feedback
Unit Tests “Redux” Easier to write Fast Isolated design feedback
Thunk tests coupled to implementation
Unit Tests “Redux” Easier to write Fast Isolated design feedback
Thunk tests coupled to implementation No interaction with the rest of the application
Integration Tests “Redux”
Integration Tests “Redux” ⚙⚙
Integration Tests “Redux” ⚙ Test reducer, actions, and API library
together ⚙
Integration Tests “Redux” ⚙ Test reducer, actions, and API library
together Test entire application ⚙
Integration Tests “Redux” ⚙ Test reducer, actions, and API library
together Test entire application ⚙
Integration Tests “Redux” ⚙ Test reducer, actions, and API library
together Test entire application More setup ⚙
Integration Tests “Redux” ⚙ Test reducer, actions, and API library
together Test entire application More setup Harder to debug ⚙
Integration Tests “Redux” ⚙ Test reducer, actions, and API library
together Test entire application More setup Harder to debug Doesn’t test user interaction ⚙
End-to-end Testing
Test entire application in browser End-to-end Testing
Test entire application in browser Simulate user interactions End-to-end Testing
Test entire application in browser Simulate user interactions Interact with
a real API (with test data) End-to-end Testing
Test entire application in browser Simulate user interactions Interact with
a real API (with test data) Focus on happy path End-to-end Testing
yarn add cypress
DEMO
E2E Tests Recap
E2E Tests Recap
E2E Tests Recap Test all pieces working together in user
scenarios
E2E Tests Recap Test all pieces working together in user
scenarios Cypress makes E2E pleasant and easier to debug
E2E Tests Recap Test all pieces working together in user
scenarios Cypress makes E2E pleasant and easier to debug
E2E Tests Recap Test all pieces working together in user
scenarios Cypress makes E2E pleasant and easier to debug Slow
E2E Tests Recap Test all pieces working together in user
scenarios Cypress makes E2E pleasant and easier to debug Slow Break from markup changes or pepper source code with identifiers
E2E Tests Recap Test all pieces working together in user
scenarios Cypress makes E2E pleasant and easier to debug Slow Break from markup changes or pepper source code with identifiers Still harder to debug than unit tests
E2E Integration Unit Snapshot $$$ $
Snapshot E2E Integration Unit $$$ $
Write tests!
Thank you! Jeremy Fairbank @elpapapollo Slides: bit.ly/react-testing-jazzcon Code: bit.ly/react-testing-jazzcon-code