Test Angular/React/Vue/Svelte

Components Without Fear

Gleb Bahmutov

Sr Director of Engineering

Shanghai’s skyline then and now

it('should show \'HOME\' and \'LOG IN\' when user is not signed in', async () => {
  (Object.getOwnPropertyDescriptor(signinServiceSpy, 'isLoggedIn')?.get as jasmine.Spy).and.returnValue(false);
  fixture.detectChanges();

  const buttonEls = await loader.getAllHarnesses(MatButtonHarness);
  expect(buttonEls).toHaveSize(2);

  const buttonTexts = await parallel(() => buttonEls.map(btn => btn.getText()));

  const expected = ['HOME', 'LOG IN'];
  expect(buttonTexts).toEqual(expected);
});

Checks the text in two elements... 🤯

import { ComponentFixture, TestBed } from '@angular/core/testing';

import { NavComponent } from './nav.component';
import { SigninService } from '../signin.service';
import { MatButtonModule } from '@angular/material/button';
import { NoopAnimationsModule } from '@angular/platform-browser/animations';
import { HarnessLoader, parallel } from '@angular/cdk/testing';
import { By } from '@angular/platform-browser';
import { TestbedHarnessEnvironment } from '@angular/cdk/testing/testbed';
import { MatButtonHarness } from '@angular/material/button/testing';

describe('NavComponent', () => {
  let component: NavComponent;
  let fixture: ComponentFixture<NavComponent>;
  let loader: HarnessLoader;

  let signinServiceSpy = jasmine.createSpyObj<SigninService>(
    ['login', 'logout'],
    ['isLoggedIn']
  );

  beforeEach(async () => {
    await TestBed.configureTestingModule({
      imports: [
        NoopAnimationsModule,
        MatButtonModule
      ],
      declarations: [ NavComponent ],
      providers: [
        { provide: SigninService, useValue: signinServiceSpy }
      ]
    })
    .compileComponents();

    fixture = TestBed.createComponent(NavComponent);
    component = fixture.componentInstance;
    fixture.detectChanges();
    loader = TestbedHarnessEnvironment.loader(fixture);
  });
  
  ...
});

Before we get to that test...

🤯🤯🤯 

Let's write a test...

Lots of custom syntax

Slow feedback loop

Cryptic errors

Maintenance

Writing Tests For Your Web UI Framework Components

AGENDA

  • The state of frontend testing
  • Use the browser
  • Examples
  • More examples
  • Even more examples
  • The End

Speaker: Gleb Bahmutov PhD

C / C++ / C# / Java / CoffeeScript / JavaScript / Node / Angular / Vue / Cycle.js / functional programming / testing

Learn how to test the web applications

using my courses at

https://cypress.tips/courses

Join others to fight the climate crisis

Gleb Bahmutov

Sr Director of Engineering

nav.component.ts

$ npm install -D cypress
{
  "devDependencies": {
    "@angular-devkit/build-angular": "^14.1.0",
    "@angular/cli": "~14.1.0",
    "@angular/compiler-cli": "^14.1.0",
    "@types/jasmine": "~4.0.0",
    "jasmine-core": "~4.2.0",
    "karma": "~6.4.0",
    "karma-chrome-launcher": "~3.1.0",
    "karma-coverage": "~2.2.0",
    "karma-jasmine": "~5.1.0",
    "karma-jasmine-html-reporter": "~2.0.0",
    "tailwindcss": "^3.1.6",
    "typescript": "~4.7.2"
  }
}

package.json

{
  "devDependencies": {
    "@angular-devkit/build-angular": "^14.1.0",
    "@angular/cli": "~14.1.0",
    "@angular/compiler-cli": "^14.1.0",
    "cypress": "~10.8.0",
    "tailwindcss": "^3.1.6",
    "typescript": "~4.7.2"
  }
}

package.json

it('adds 2 todos', () => {
  cy.visit('http://localhost:4200')
  cy.get('.new-todo')
    .type('learn testing{enter}')
    .type('be cool{enter}')
  cy.get('.todo-list li')
    .should('have.length', 2)
})
import { defineConfig } from "cypress";

export default defineConfig({
  component: {
    devServer: {
      framework: "angular",
      bundler: "webpack",
    },
    specPattern: "**/*.cy.ts",
  },
});

cypress.config.ts

import { defineConfig } from "cypress";

export default defineConfig({
  component: {
    devServer: {
      framework: "angular",
      bundler: "webpack",
    },
    specPattern: "**/*.cy.ts",
  },
});

cypress.config.ts

Configuration

Let's test nav.component.ts

import { NavComponent } from './nav.component'

describe('NavComponent', () => {
  it('should create and show the links', () => {
    cy.mount(NavComponent)

    cy.contains('a', 'HOME')
    cy.contains('button', 'LOG IN').should('be.visible')
      .wait(1000).click()

    cy.contains('a', 'HOME')
    cy.contains('a', 'PROFILE').should('be.visible')
    cy.contains('button', 'LOG OUT').should('be.visible')
      .wait(1000).click()

    cy.contains('a', 'HOME')
    cy.contains('button', 'LOG IN').should('be.visible')
  })
})

nav.component.cy.ts

  • speed
  • real browser
  • DOM snapshots
  • DevTools

See it run

import { NavComponent } from './nav.component'

describe('NavComponent', () => {
  it('should create and show the links', () => {
    cy.mount(NavComponent)

    cy.contains('a', 'HOME')
    cy.contains('button', 'LOG IN').should('be.visible')
      .wait(1000).click()

    cy.contains('a', 'HOME')
    cy.contains('a', 'PROFILE').should('be.visible')
    cy.contains('button', 'LOG OUT').should('be.visible')
      .wait(1000).click()

    cy.contains('a', 'HOME')
    cy.contains('button', 'LOG IN').should('be.visible')
  })
})

nav.component.cy.ts

Mount the framework component

import { NavComponent } from './nav.component'

describe('NavComponent', () => {
  it('should create and show the links', () => {
    cy.mount(NavComponent)

    cy.contains('a', 'HOME')
    cy.contains('button', 'LOG IN').should('be.visible')
      .wait(1000).click()

    cy.contains('a', 'HOME')
    cy.contains('a', 'PROFILE').should('be.visible')
    cy.contains('button', 'LOG OUT').should('be.visible')
      .wait(1000).click()

    cy.contains('a', 'HOME')
    cy.contains('button', 'LOG IN').should('be.visible')
  })
})

nav.component.cy.ts

Regular Cypress commands

Batteries included

export class NavComponent {

  constructor(public signinService: SigninService) { }

  public login(): void {
    this.signinService.login();
  }

  public logout(): void {
    this.signinService.logout();
  }
}

nav.component.ts

import { NavComponent } from './nav.component'
import { SigninService } from '../signin.service'

describe('NavComponent', () => {
  it('should create and show the links', () => {
    const signinService = new SigninService()
    cy.spy(signinService, 'login').as('login')
    cy.spy(signinService, 'logout').as('logout')
    cy.mount(NavComponent, {
      componentProperties: {
        signinService,
      },
    })

    cy.contains('a', 'HOME')
    cy.contains('button', 'LOG IN').should('be.visible')
      .wait(1000).click()
    cy.get('@login').should('have.been.called')

    cy.contains('a', 'HOME')
    cy.contains('a', 'PROFILE').should('be.visible')
    cy.contains('button', 'LOG OUT').should('be.visible')
      .wait(1000).click()
    cy.get('@logout').should('have.been.called')

    cy.contains('a', 'HOME')
    cy.contains('button', 'LOG IN').should('be.visible')
  })
})

nav.component.cy.ts

Test syntax

const template = `
  <div class="my-9 bg-zinc-50 border border-slate-400 rounded-lg">
    <app-email-subscription (emailSubscription)="onEmailSubscription($event)"></app-email-subscription>
  </div>
`
cy.mount(template, {
  declarations: [EmailSubscriptionComponent],
  imports: [
    NoopAnimationsModule,
    FormsModule,
    MatFormFieldModule,
    MatInputModule,
    MatSlideToggleModule,
    MatButtonModule,
    MatIconModule,
  ],
  componentProperties: {
    onEmailSubscription: cy.stub().as('onEmailSubscription'),
  },
})
const email = 'email@email.email'
cy.get('input:checkbox[role=switch]').should('be.disabled')
cy.get('input[type=email]').type(email)
cy.get('input:checkbox[role=switch]').should('be.enabled')
// needs a better selector
cy.contains('button', 'add_box').click()
cy.get('@onEmailSubscription').should('be.calledOnceWithExactly', {
  email,
  subscribe: true,
})

email-subscription.cy.ts

Email subscription component test

What about React?

import React from 'react'
import { Timer } from './Timer'

it('shows the time', () => {
  cy.mount(<Timer />)
  cy.contains('00:00')
})

Timer.cy.ts

import React from 'react'
import { Timer } from './Timer'
import '../App.css'
import { SudokuContext } from '../context/SudokuContext'
import moment from 'moment'

it('sets the clock to the given value', () => {
  const timeGameStarted = moment().subtract(900, 'seconds')

  cy.mount(
    <SudokuContext.Provider value={{ timeGameStarted }}>
      <section className="status">
        <Timer />
      </section>
    </SudokuContext.Provider>,
  )
  cy.contains('15:00')
})

Timer.cy.ts

The Timer component with applied styling

No more framework-specific syntax

import React from "react";
import { render, unmountComponentAtNode } from "react-dom";
import { act } from "react-dom/test-utils";

import Toggle from "./toggle";

let container = null;
beforeEach(() => {
  // setup a DOM element as a render target
  container = document.createElement("div");
  document.body.appendChild(container);
});

afterEach(() => {
  // cleanup on exiting
  unmountComponentAtNode(container);
  container.remove();
  container = null;
});

it("changes value when clicked", () => {
  const onChange = jest.fn();
  act(() => {
    render(<Toggle onChange={onChange} />, container);
  });

  // get a hold of the button element, and trigger some clicks on it
  const button = document.querySelector("[data-testid=toggle]");
  expect(button.innerHTML).toBe("Turn on");

  act(() => {
    button.dispatchEvent(new MouseEvent("click", { bubbles: true }));
  });

  expect(onChange).toHaveBeenCalledTimes(1);
  expect(button.innerHTML).toBe("Turn off");

  act(() => {
    for (let i = 0; i < 5; i++) {
      button.dispatchEvent(new MouseEvent("click", { bubbles: true }));
    }
  });

  expect(onChange).toHaveBeenCalledTimes(6);
  expect(button.innerHTML).toBe("Turn on");
});
import React from "react";
import Toggle from "./toggle";

it("changes value when clicked", () => {
  cy.mount(<Toggle onChange={cy.stub().as('change')} />);

  // get a hold of the button element, and trigger some clicks on it
  cy.contains("[data-testid=toggle]", "Turn on").click()
  cy.get('@change').should('have.been.calledOnce')
  cy.contains("[data-testid=toggle]", "Turn off")
    .click()
    .click()
    .click()
    .click()
    .click()

  cy.get('@change').its('callCount').should('eq', 6)
  cy.contains("[data-testid=toggle]", "Turn on")
});

equivalent Cypress component test

https://on.cypress.io/api

No more framework-specific syntax

import React from "react";
import { render, unmountComponentAtNode } from "react-dom";
import { act } from "react-dom/test-utils";

import Toggle from "./toggle";

let container = null;
beforeEach(() => {
  // setup a DOM element as a render target
  container = document.createElement("div");
  document.body.appendChild(container);
});

afterEach(() => {
  // cleanup on exiting
  unmountComponentAtNode(container);
  container.remove();
  container = null;
});

it("changes value when clicked", () => {
  const onChange = jest.fn();
  act(() => {
    render(<Toggle onChange={onChange} />, container);
  });

  // get a hold of the button element, and trigger some clicks on it
  const button = document.querySelector("[data-testid=toggle]");
  expect(button.innerHTML).toBe("Turn on");

  act(() => {
    button.dispatchEvent(new MouseEvent("click", { bubbles: true }));
  });

  expect(onChange).toHaveBeenCalledTimes(1);
  expect(button.innerHTML).toBe("Turn off");

  act(() => {
    for (let i = 0; i < 5; i++) {
      button.dispatchEvent(new MouseEvent("click", { bubbles: true }));
    }
  });

  expect(onChange).toHaveBeenCalledTimes(6);
  expect(button.innerHTML).toBe("Turn on");
});
import React from "react";
import Toggle from "./toggle";

it("changes value when clicked", () => {
  cy.mount(<Toggle onChange={cy.stub().as('change')} />);

  // get a hold of the button element, and trigger some clicks on it
  cy.contains("[data-testid=toggle]", "Turn on").click()
  cy.get('@change').should('have.been.calledOnce')
  cy.contains("[data-testid=toggle]", "Turn off")
    .click()
    .click()
    .click()
    .click()
    .click()

  cy.get('@change').its('callCount').should('eq', 6)
  cy.contains("[data-testid=toggle]", "Turn on")
});

equivalent Cypress component test

https://on.cypress.io/api

One Ring API

To Rule

Them All

Follow: Murat Ozcan

Each React component has

  • React Testing Library spec
  • Cypress component spec

A huge collection of various React testing examples with matching Cypress component specs

A Testing

Pyramid of Component Tests

Timer

Numbers

Difficulty

StatusSection

GameSection

Game

App

Overlay

import { Game } from './Game'
import { SudokuProvider } from './context/SudokuContext'
import { WinProvider } from './context/WinContext'
import { starting, solved } from '../cypress/fixtures/sudoku.json'

it('plays the game', () => {
  cy.mount(
    <SudokuProvider>
      <WinProvider>
        <Game initArray={starting} solvedArray={solved} />
      </WinProvider>
    </SudokuProvider>,
  )
  cy.get('.game__cell:not(.game__cell--filled)').should(
    'have.length',
    3,
  )
  starting.forEach((cell, index) => {
    if (cell === '0') {
      cy.get('.game__cell').eq(index).click()
      cy.contains('.status__number', solved[index])
        .click()
        .wait(500, { log: false })
    }
  })

  cy.contains('.overlay__text', 'You solved it').should('be.visible')
})

src/Game.cy.js

import { Game } from './Game'
import { SudokuProvider } from './context/SudokuContext'
import { WinProvider } from './context/WinContext'
import { starting, solved } from '../cypress/fixtures/sudoku.json'

it('plays the game', () => {
  cy.mount(
    <SudokuProvider>
      <WinProvider>
        <Game initArray={starting} solvedArray={solved} />
      </WinProvider>
    </SudokuProvider>,
  )
  cy.get('.game__cell:not(.game__cell--filled)').should(
    'have.length',
    3,
  )
  starting.forEach((cell, index) => {
    if (cell === '0') {
      cy.get('.game__cell').eq(index).click()
      cy.contains('.status__number', solved[index])
        .click()
        .wait(500, { log: false })
    }
  })

  cy.contains('.overlay__text', 'You solved it').should('be.visible')
})

src/Game.cy.js

import { Game } from './Game'
import { SudokuProvider } from './context/SudokuContext'
import { WinProvider } from './context/WinContext'
import { starting, solved } from '../cypress/fixtures/sudoku.json'

it('plays the game', () => {
  cy.mount(
    <SudokuProvider>
      <WinProvider>
        <Game initArray={starting} solvedArray={solved} />
      </WinProvider>
    </SudokuProvider>,
  )
  cy.get('.game__cell:not(.game__cell--filled)').should(
    'have.length',
    3,
  )
  starting.forEach((cell, index) => {
    if (cell === '0') {
      cy.get('.game__cell').eq(index).click()
      cy.contains('.status__number', solved[index])
        .click()
        .wait(500, { log: false })
    }
  })

  cy.contains('.overlay__text', 'You solved it').should('be.visible')
})

src/Game.cy.js

src/Game.cy.js

import React, { useState, useEffect } from 'react'
import { formatTime } from './Timer'

const useFetch = (url) => {
  const [data, setData] = useState([])
  const [loading, setLoading] = useState(url ? true : false)

  async function fetchData() {
    if (url) {
      const response = await fetch(url)
      const json = await response.json()
      setData(json)
      setLoading(false)
    }
  }

  useEffect(() => {
    if (!url) {
      return
    }
    fetchData()
  }, [url])

  return { loading, data }
}

export const Overlay = (props) => {
  const { loading, data } = useFetch(
    props.overlay && props.time ? '/times/' + props.time : null,
  )
  const className = props.overlay
    ? 'overlay overlay--visible'
    : 'overlay'
  return (
    <div className={className} onClick={props.onClickOverlay}>
      <h2 className="overlay__text">
        <div className="overlay__greeting">
          You <span className="overlay__textspan1">solved</span>{' '}
          <span className="overlay__textspan2">it!</span>
        </div>
        {loading && (
          <div className="overlay__loading">Loading...</div>
        )}

        {data.length > 0 && (
          <ul className="overlay__times">
            {data.map((item, index) => {
              return (
                <li
                  key={index}
                  className={item.current ? 'overlay__current' : ''}
                >
                  {formatTime(item)}
                </li>
              )
            })}
          </ul>
        )}
      </h2>
    </div>
  )
}

src/components/Overlay.js

import React, { useState, useEffect } from 'react'
import { formatTime } from './Timer'

const useFetch = (url) => {
  const [data, setData] = useState([])
  const [loading, setLoading] = useState(url ? true : false)

  async function fetchData() {
    if (url) {
      const response = await fetch(url)
      const json = await response.json()
      setData(json)
      setLoading(false)
    }
  }

  useEffect(() => {
    if (!url) {
      return
    }
    fetchData()
  }, [url])

  return { loading, data }
}

export const Overlay = (props) => {
  const { loading, data } = useFetch(
    props.overlay && props.time ? '/times/' + props.time : null,
  )
  const className = props.overlay
    ? 'overlay overlay--visible'
    : 'overlay'
  return (
    <div className={className} onClick={props.onClickOverlay}>
      <h2 className="overlay__text">
        <div className="overlay__greeting">
          You <span className="overlay__textspan1">solved</span>{' '}
          <span className="overlay__textspan2">it!</span>
        </div>
        {loading && (
          <div className="overlay__loading">Loading...</div>
        )}

        {data.length > 0 && (
          <ul className="overlay__times">
            {data.map((item, index) => {
              return (
                <li
                  key={index}
                  className={item.current ? 'overlay__current' : ''}
                >
                  {formatTime(item)}
                </li>
              )
            })}
          </ul>
        )}
      </h2>
    </div>
  )
}

src/components/Overlay.js

Stub window.fetch?

Stub some import?

Stub method in some internal class?

it('shows the loading element', () => {
  cy.intercept('GET', '/times/90', {
    delay: 1000,
    statusCode: 404,
    body: [],
  }).as('times')
  cy.mount(<Overlay overlay={true} time={90} />)
  cy.contains('.overlay__loading', 'Loading').should('be.visible')
  cy.wait('@times')
  cy.get('.overlay__loading').should('not.exist')
})
it('shows the loading element', () => {
  cy.intercept('GET', '/times/90', {
    delay: 1000,
    statusCode: 404,
    body: [],
  }).as('times')
  cy.mount(<Overlay overlay={true} time={90} />)
  cy.contains('.overlay__loading', 'Loading').should('be.visible')
  cy.wait('@times')
  cy.get('.overlay__loading').should('not.exist')
})
it('shows the top times', () => {
  cy.intercept('GET', '/times/90', {
    fixture: 'times.json',
  }).as('scores')
  cy.mount(<Overlay overlay={true} time={90} />)
  cy.wait('@scores')
  cy.get('.overlay__times li').should('have.length', 4)
  cy.contains('.overlay__times li', '01:30').should(
    'have.class',
    'overlay__current',
  )
})
cy.intercept('GET', '/times/90', {
  fixture: 'times.json',
}).as('scores')
cy.mount(<Overlay overlay={true} time={90} />)
cy.wait('@scores')

stub the

external APIs

Svelte Example

Svelte Example

import Stepper from './Stepper.svelte'

it('when clicking increment and decrement', () => {
  cy.mount(Stepper, { props: { count: 100 } })
  cy.get(counterSelector).should('have.text', '100')
  cy.get(incrementSelector).click()
  cy.get(counterSelector).should('have.text', '101')
  cy.get(decrementSelector).click().click()
  cy.get(counterSelector).should('have.text', '99')
})

Stepper.cy.js

https://docs.cypress.io/

Vue Example

import Stepper from './Stepper.vue'

it('shows the initial count', () => {
  cy.mount(Stepper, { props: { initial: 100 } })
  cy.get(counterSelector).should('have.text', '100')
  cy.mount(<Stepper initial={101} />)
  cy.get(counterSelector).should('have.text', '101')
})

Stepper.cy.jsx

https://docs.cypress.io/

Vue Example

  • Real browser
  • Real component
  • Full Cypress API
  • All Cypress plugins
  • File watching
  • DOM snapshots, videos
  • Running on CI

Cypress Component Testing

  • Real browser
  • Real component
  • Full Cypress API
  • All Cypress plugins
  • File watching
  • DOM snapshots, videos
  • Running on CI

Cypress Component Testing

Cypress

Component

Testing

  • Code coverage
  • Imports stubbing

Cypress Component Testing Downsides

Requires webpack / vite configuration

👏 Thank You 👏

Gleb Bahmutov

Sr Director of Engineering

☝️ these slides ☝️

Test Angular/React/Vue/Svelte Components Without Fear

By Gleb Bahmutov

Test Angular/React/Vue/Svelte Components Without Fear

Writing tests for your components (be it Angular, React, Vue, or Svelte components) is often a horror show. Your code in (js-dom) darkness, there are dangers behind each action, and the most beautiful tests get banged up beyond recognition when they try to cross into the CI realm. In this talk, I will show how Cypress component testing becomes a ray of hope guiding you toward testing nirvana. These tests remove most framework-specific test code while focusing on how the component behaves on the page. I will use examples from different frameworks to teach everyone how to test the modern front-end code without fear or pain.

  • 587