Writing tests
In this guide, we'll walk through writing test for a custom
Input component.We also have included the User Event package to make writing tests that need simulating user events easier and more readable.
In the past we have used Enzyme for testing, and a lot of tests still uses it, but do try to write your tests using the above.
Tips
- Avoid testing implementation details (internal
statefor example) that enzyme tends to encourage.
Directory
All of HSDS's component test files are scoped in the same directory as the component, example:
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hsds-react/
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└── components/
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└── Input/
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└── Input.test.js
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Base test code
In our
Input.test.js file, we'll need to add:1
import React from 'react'
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import { render, waitFor } from '@testing-library/react'
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import user from '@testing-library/user-event'
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import Input from '../Input'
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describe('Input', () => {
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test('Should render', () => {
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const { getByLabelText } = render(<Input name="user" />)
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expect(getByLabelText('user')).toBeInTheDocument()
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expect(getByLabelText('user').classList.contains('c-Input')).toBe(true)
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})
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// Example of a test with user interaction
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test('Should fire on change event when typing', async () => {
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const spy = jest.spy()
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const { getByLabelText } = render(<Input name="user" onChange={spy} />)
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const input = getByLabelText('user')
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user.type(input, 'hola')
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// You don't always need to "waitFor" after the event simulation
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await waitFor(() => {
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expect(input.value).toBe('hola')
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expect(spy).toHaveBeenCalled()
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})
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})
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})
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Test development
For test development, open up your terminal and run the following command:
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npm run dev
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This fires up Jest in watch mode, and runs tests against modified files (and their associated files).
Code coverage
Coverage report, generated by Jest
To check code coverage, run the following command:
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npm run test
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hsds-react/
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└── coverage/
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└── lcov-report/
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└── index.html
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You can open the
index.html in your browser to view the full report.Coverage
We strive to have as much coverage as posible, and for that purpose we set the threshold at 95% coverage.
Why not 100%? 100% coverage is a false metric and it does not indicate whether your component is properly tested, and while we maintained 100% coverage for a long period we noticed an excessive usage of
istanbul ignore directives, this wasn't because of lazyness but because some things are close to impossible to test in the Jest/JSDOM environment or because istanbul couldn't reach the code for some reason.Next
See also
Last modified 1yr ago