next.js and Cypress example

Next.js example instrumented for code coverage from Cypress tests

Install and run

npm install
npm run e2e

This starts the application at localhost:3000 and opens Cypress test runner.

Click on the spec file to run the end-to-end tests.

Coverage

The tests are instrumented following the instructions in Cypress code coverage guide. In particular, the front-end is instrumented using .babelrc file like

{
  "presets": ["next/babel"],
  "plugins": ["istanbul"]
}

When you run tests, the code coverage report is saved in coverage folder. There are reports in several formats, but open the HTML one for human-readable report.

$ open coverage/lcov-report/index.html

To fetch the server-side code coverage, the @cypress/code-coverage plugin needs an endpoint. This endpoint is implemented in pages/api/coverage.js file following the Next.js API convention. This endpoint just returns the existing global coverage object or null

export default (req, res) => {
  res.status(200).json({
    coverage: global.__coverage__ || null
  })
}

Cypress plugin requests the right endpoint using the environment variable from cypress.json file

{
  "baseUrl": "http://localhost:3000",
  "env": {
    "codeCoverage": {
      "url": "/api/__coverage__"
    }
  }
}

On CI after the tests finish, we store the coverage reports. We also run a script to check if the coverage dropped below 100%

$ npx nyc report --reporter=text-summary --check-coverage --statements 100
================== Coverage summary =========
Statements   : 100% ( 22/22 )
Branches     : 100% ( 0/0 )
Functions    : 100% ( 9/9 )
Lines        : 100% ( 22/22 )
=============================================

See more

• Cypress code coverage guide

Small print

Author: Gleb Bahmutov <[email protected]> © 2019

• @bahmutov
• glebbahmutov.com
• blog

License: MIT - do anything with the code, but don't blame me if it does not work.

Support: if you find any problems with this module, email / tweet / open issue on Github

MIT License

Copyright (c) 2019 Gleb Bahmutov <[email protected]>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.