Testing with Cypress
and Jest

Introduction

Types of Tests + Frameworks

  • Unit Tests
    • Test a single logical unit, isolated
    • Framework examples: Jasmine 🔗, Jest 🔗, Mocha 🔗
  • API Tests
    • Test Web APIs
    • Framework/tool examples: Postman 🔗
  • Load Tests
    • Test scalability and performance under load
    • Framework/tool examples: JMeter 🔗, Azure Load Testing 🔗
  • End-to-end testing
    • Simulate end user interaction by remote-controlling browser
    • Framework/tool examples: Webdriver 🔗, Cypress 🔗
  • See also State of JS 🔗

Webdriver vs. Cypress

  • Webdriver
    • Remote-control browser
    • Works over network
    • W3c recommendation
    • Works with all major browsers
    • Widely used (incl. large component vendors 🔗)
  • Cypress
    • E2e testing web applications while they are under development 🔗
    • Browser plugin, controlled by Node process 🔗
    • Locally installed, full control over host system
    • Open-source with liable-to-cost extras

Cypress Limitations 🔗

  • Limited browser support (Firefox, Chrome-family) 🔗
  • Cypress test run in the browser
    • Cannot directly import server-side libraries in test code
    • Options: Write plugins 🔗, use Node tasks 🔗
  • No/limited multi-tab and multi-browser support

What's unique about Cypress?

  • Fine control over browser because Cypress runs inside the browser
  • Snapshots after each command
    • Relatively easy to diagnose problems
  • No need for writing async code manually
    • Cypress specs build test commands
    • Cypress commands are queued and
      asynchronously executed at a later time 🔗
    • Async behavior (e.g. waiting) is built-in

Get Started!

Install Cypress 🔗,
optionally install recommended VSCode extensions 🔗,
add Cypress to Angular 🔗

Cypress CLI 🔗

Command Description
cypress open Opens the Cypress app
cypress run Runs Cypress tests (headlessly)
cypress info Prints information about Cypress environment
cypress verify Checks Cypress installation
cypress version Prints version info

Demo
Time!

Exercise: First E2E Test

# Create new folder, navigate to it
npm init
npm install -D cypress
# Add npm script for `cypress open` and `cypress run`

# Start cypress
# Select E2e -> configures your cy environment

# Generate new, empty spec for Chrome
describe('My First Test', () => {
  it('Does not do much!', () => {
    expect(true).to.equal(true)
  })
})
# Run test
# Change test so that it fails
# Rerun test

Exercise: First E2E Test

describe('My First Test', () => {
  it('Gets, types and asserts', () => {
    cy.visit('https://example.cypress.io')

    cy.contains('type').click()

    // Should be on a new URL which
    // includes '/commands/actions'
    cy.url().should('include', '/commands/actions')

    // Get an input, type into it and verify
    // that the value has been updated
    cy.get('#email1')
      .type('fake@email.com')
      .should('have.value', 'fake@email.com')
  })
})
# Run test
# Change test so that it fails
# Rerun test

Exercise: First E2E Test

# Install typescript
npm install -D typescript

# Add tsconfig.json in `cypress` folder 
{
  "compilerOptions": {
    "target": "es5",
    "lib": ["es5", "dom"],
    "types": ["cypress", "node"]
  },
  "include": ["**/*.ts"]
}
# Rename spec.cy.js to .ts

# Reopen cypress to see TypeScript test running

Selection, Naviation

$

Hello jQuery

  • Cypress bundles jQuery 🔗
  • cy.get() is like $('...')
    • Returns Chainable<T>
    • Many methods of Chainable behave exactly like jQuery counterparts
    • E.g. cy's find 🔗 and  jQuery's find 🔗
    • Learn more by learning jQuery's tree traversal functions 🔗
      • jQuery Cheat Sheet 🔗
  • Cypress selectors are like jQuery's selectors 🔗
    • Best practices for Cypress selectors 🔗
    • TL;DR: Use data-* attributes wherever possible
  • Access jQuery directly using Cypress.$ 🔗 
<!-- HTML -->
<button id="main" class="btn btn-large" name="submission"
        role="button" data-testid="submit">
  Submit
</button>

// Cypress
cy.get('[data-testid="submit"]').click();

Asynchronous Operations

  • Cypress wraps all DOM queries with retry-and-timeout logic
    • ⚠️ Make sure your testing code is idempotent
  • No error if e.g. ...
    • ...DOM not yet loaded
    • ...XHR not finished
    • ...framework bootstrapping in progress
  • Customize timeouts if necessary 🔗
    • Option: cy.get('...', { timeout: 10000 })
  • Get DOM element once it becomes available: .then 🔗
    • Note Cypress.$ has to be executed in .then 🔗

Demo
Time!

Exercise: Querying

<!-- app.component.html -->

<hello name="{{ name }}"></hello>
<p>Start editing to see some magic happen :)</p>

<button data-test-cy="main-button">Do something</button>

it('Querying', () => {
  cy.visit('https://angular-ivy-saxmjf.stackblitz.io')

  cy.get('#promptToRun', { timeout: 600000 }).find('button').click()

  cy.get('[data-test-cy="main-button"]')
    .should('have.text', 'Do something')
})

Interactions

Interacting with elements

  • Clicking, typing 🔗
  • State of element is checked before interaction 🔗
  • Complex drag-and-drop interactions with .trigger 🔗
  • Tip: Use .as to create an alias for later access to subject 🔗

Assertations

  • Assertations comes from bundled libraries like Chai
  • Default and explicit assertations
    • Default assertations 🔗
    • Use .should('not.exist') to reverse assertations
  • Full list of assertations 🔗
  • Assertations in command chain
    • .should()
    • .and()
  • Assertations with explicit subjects 🔗
    • expect()

Demo
Time!

Exercise: TS, Cmds, Interactions

  • Delete/remove support/commands.js
  • Create folder support/commands
  • Create index.d.ts in support folder
export {};

declare global {
  namespace Cypress {
    interface Chainable {
      skipStackblitzProtection(): Chainable<Element>;
    }
  }
}

Exercise: TS, Cmds, Interactions

  • Create skipStackblitzProtection.ts in support/commands 
Cypress.Commands.add('skipStackblitzProtection', () => { 
    cy.get('#promptToRun', { timeout: 600000 }).find('button').click();
});
  • Change support/e2e.js
import "./commands/skipStackblitzProtection";

Exercise: TS, Cmds, Interactions

it('Querying', () => {
  cy.visit('https://angular-ivy-saxmjf.stackblitz.io')

  cy.skipStackblitzProtection()

  cy.get('[data-test-cy="main-button"]')
    .should('have.text', 'Do something')
})

it('Calculates correctly', () => {
  cy.visit('https://angular-basic-calculator.stackblitz.io/')

  cy.get('.button-1').as('1').click()
  cy.get('.button-0').click()
  
  cy.get('.button-a').click()
  cy.get('@1').click()
  
  cy.get('.equals').click()
  
  cy.get('.display').should('have.text', 10 + 1)
})

Test Organization

Folders 🔗

Folder Description
e2e Test files
fixtures Static data used by tests
support Support files running before each spec

Organize Tests

  • Folder for each page
    • E.g. orders, settings, account
  • Inside, spec for each test use case
    • E.g. account/register_spec.js
    • Test structure 🔗
  • `shared` folder for shared component tests
    • E.g. header bar

Troubleshooting Tests

Troubleshooting Tests 🔗

  • Use the debugger, it just works
  • Check the browser's console window
    • Also when clicking on commands like .type()
  • Use .debug() to trigger breakpoint and get detailed information about a yielded object
  •  

Server

Dealing with Server

  • Dealing with servers is tricky
    • E.g. logging in, persistence layer
  • Strategy: Stub all server requests 🔗
    • No longer e2e, a lot of work
    • Often pays off
  • Strategy: Seeded data on the server 🔗
    • E.g. pre-created user, well-defined test data 🔗
    • Cypress has certain auth server built-in 🔗
    • Real e2e
    • ⚠️ Tests might influence each other
  • Strategy: Setup unique data before each test
    • A lot of work, not simple
  • Mix strategies as you like/need

Stubbing Requests

  • Intercepting requests with .intercept() 🔗
  • Use fixtures for pre-recorded responses 🔗
  • Wait for expected requests 🔗

Jest

Jest

  • Modern, fast, widely used testing framework for JS/TS
  • Use jest-preset-angular for Jest + Angular🔗
  • Simple Jasmine tests work without any changes
    • it is alias for Jest's test 🔗
  • Pros 👍
    • Fine testing framework with great API
    • No need for Karma
    • Well documented
    • Widely used
  • Cons 👎
    • Doesn't come out of the box in Angular
    • Requires extra dependencies

Demo
Time!

Jest in Angular

  • Remove Jasmine and Karma from package.json
  • Remove karma.conf.js and src/test.ts
  • Remove test area from angular.json
  • Install Jest 🔗
    • npm install --save-dev jest jest-preset-angular @types/jest
  • Configure jest-preset-angular as shown in 🔗
  • Set "esModuleInterop": true in tsconfig.json
  • Replace ng test with jest in package.json script
  • Good summary of whole process in 🔗

Expects and Matchers 🔗

  • Expect return expectation object 🔗
  • Call matchers on expectation object
  • Async code 🔗
    • Call expect/matchers in .then()
    • Use async/await

Setup and Teardown 🔗

  • Use before/afterEach for setup and teardown per test
  • Use before/afterAll for one-time setup and teardown per file
  • Group tests using describe
    • ​Setup/teardown methods are scoped in test group
  • Use beforeEach to configure TestBed in Angular 🔗

Mocking 🔗

  • Jest can mock functions and modules
  • Can partly be used to replace Angular's mocking features
  • Consider ng-mocks 🔗
  • Reference:

Further topics

  • Snapshot testing 🔗
    • Renders HTML or UI component
    • Compares against baseline
    • Problem: Changes in rendered HTML (particularly 3rd party controls)
    • Alternative: Angular DOM testing, e2e testing
  • Timer mocks 🔗
    • Replace JS's timeout/interval functions
    • Control timers programmatically to speed up long-running tests
    • Reference: Fake Timers 🔗

cypress-testing

By Rainer Stropek

cypress-testing

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