Is Cypress for unit tests or not?

[GaTechThomas]

When I go to the intro "how it works" page, the page says:

Cypress is not a general automation framework, nor is it a unit testing framework for your back end services. There are already great tools out there that do that. Rather, we specialize in one thing - creating a great experience while you write end to end tests for your web applications.

But then the "Who uses Cypress" info says:

Our users are typically developers or QA engineers building web applications using modern JavaScript frameworks.

Cypress enables you to write all types of tests:

• End-to-end tests
• Integration tests
• Unit tests

Cypress can test anything that runs in a browser.

Please help me to understand how both statements can be true.

[bahmutov]

Sure, a great question that has its own documentation issue here cypress-io/cypress-documentation#1502

For unit tests, it depends what the code does and what environment it expects to be able to execute. For example, you can test browser-specific code like window.btoa function. Cypress can execute the following unit test

it('converts string to base64', () => {
  expect(window.btoa('foo')).to.equal('Zm9v')
})

You can also write a unit test for isomorphic or universal code that can run both in the browser and in Node. Cypress will happily run such tests

import {add} from './my/math'
it('adds two numbers', () => {
  expect(add(2, 3)).to.equal(5)
})

But what Cypress cannot do is to run unit tests for any code that needs Node environment - because Cypress executes the tests in the browser.

const fs = require('fs')
it('reads a file', () => {
   // NOPE, NOT GOING TO WORK
  fs.readFileSync('file.txt', 'utf8')
})

This is why we say that Cypress can run all sorts of tests - as long as the code or the application is meant to run in the browser.

For more, see this presentation https://slides.com/bahmutov/no-excuses#/5 (click down to go through the slides) and https://slides.com/bahmutov/write-a-cypress-test#/only-tests (again, click the down arrow to go through the slides)

[GaTechThomas]

Thank you! Fantastic answer.