cypress-and-jest

Demo unit tests with code coverage from both Cypress and Jest

Use

# install and run tests
$ npm it
# runs Jest and Cypress tests headlessly
# generates combined code coverage report
$ open coverage/lcov-report/index.html

The application source code is just a single file src/calc.js. Let's cover this file with unit tests by using two test runners: Jest and Cypress.

Jest init

The Jest setting were initialized using npx jest --init command:

In the generated jest.config.js enable code coverage collection, and output into folder jest-coverage (to avoid clashing with Cypress coverage report).

// jest.config.js
module.exports = {
  // Indicates whether the coverage information should be collected while executing the test
  collectCoverage: true,
  // The directory where Jest should output its coverage files
  coverageDirectory: 'jest-coverage',
  // The test environment that will be used for testing
  testEnvironment: 'node'
}

The Jest unit tests are in the file tests/calc.test.js and the tests only run the add function. We can run the Jest tests and see the coverage summary.

The coverage reports in jest-coverage folder by default include JSON, LCOV and static HTML reports. The HTML report shows that the function sub was not reached by the Jest tests.

Cypress init

First install Cypress

$ npm install -D cypress

Initialize Cypress folder with npx @bahmutov/cly init command.

In cypress/integration/spec.js let's require sub function and test it

// cypress/integration/spec.js
const { sub } = require('../../src/calc')
it('subtracts 10 - 5', () => {
  expect(sub(10, 5)).to.equal(5)
})

The test passes

Cypress code coverage setup

Code coverage in Cypress is done via @cypress/code-coverage plugin. I suggest following the installation instructions in that repo.

First, install the plugin and babel-plugin-istanbul to instrument code.

npm i -D @cypress/code-coverage babel-plugin-istanbul

Add to your cypress/support/index.js file:

import '@cypress/code-coverage/support'

Register tasks in your cypress/plugins/index.js file:

module.exports = (on, config) => {
  require('@cypress/code-coverage/task')(on, config)
  on('file:preprocessor', require('@cypress/code-coverage/use-browserify-istanbul'))
  return config
}

Because we saved the Jest coverage report in jest-coverage, set Cypress to save its coverage to cypress-coverage. Since nyc is used to generate the report, add nyc object to package.json file.

{
  "nyc": {
    "report-dir": "cypress-coverage"
  }
}

Run Cypress with npx cypress open and a report should be saved. As you can see, we have missed the add function!

Merge coverage reports

We have two folders with coverage reports generated by Jest and Cypress.

$ ls -la *-coverage
cypress-coverage:
total 24
drwxr-xr-x   6 gleb  staff   204 Jul 22 23:04 .
drwxr-xr-x  20 gleb  staff   680 Jul 22 23:05 ..
-rw-r--r--   1 gleb  staff   744 Jul 22 23:05 clover.xml
-rw-r--r--   1 gleb  staff  1000 Jul 22 23:05 coverage-final.json
drwxr-xr-x  10 gleb  staff   340 Jul 22 23:04 lcov-report
-rw-r--r--   1 gleb  staff   201 Jul 22 23:05 lcov.info

jest-coverage:
total 24
drwxr-xr-x   6 gleb  staff   204 Jul 22 21:00 .
drwxr-xr-x  20 gleb  staff   680 Jul 22 23:05 ..
-rw-r--r--   1 gleb  staff   744 Jul 22 23:05 clover.xml
-rw-r--r--   1 gleb  staff  1000 Jul 22 23:05 coverage-final.json
drwxr-xr-x  10 gleb  staff   340 Jul 22 21:00 lcov-report
-rw-r--r--   1 gleb  staff   201 Jul 22 23:05 lcov.info

Let's combine the two reports and generate the final report. There is a script in package.json that does just that. It copies cypress-coverage/coverage-final.json and jest-coverage/coverage-final.json into a folder, runs nyc merge command, the creates the combined report using nyc report ... command.

$ npm run report:combined
...

coverage files in reports merged into coverage.json

> [email protected] report:combined /Users/gleb/git/cypress-and-jest
> nyc report --reporter lcov --report-dir coverage

The final HTML report shows that we have reached all source statements in calc.js file.

Coverage CI artifact

You can store the produced static HTML report on your continuous integration server. For example see .circleci/config.yml file.

More info

• Cypress code coverage guide
• @cypress/code-coverage plugin