Implementing code coverage with Angular and Cypress
*last updated in December 2022
E2E testing is an essential task in producing high quality software and an elementary component of any good CI/CD process.
Cypress is the go-to choice E2E testing framework for many Angular users. To make sure all your critical code is actually covered with tests, you need to generate code coverage reports.
This article is part of my Angular DevOps series on Medium (more at the end of the page). Here I will provide a step-by-step tutorial in implementing code coverage for your Angular + Cypress application.
For this tutorial, we assume you have an existing Angular 9+ application (9.x, 10.x, 11.x, 12.x, 13.x, 14.x) and you are running Node v16. If you haven’t done so yet, configure Cypress as the E2E framework for your Angular application by adding the Cypress Angular Schematic to your project:
ng add @cypress/schematic
When prompted, confirm the default command. Now, you’re ready to go for the Angular + Cypress goodness:
1. Instrumenting your project
For the Cypress code coverage plugin to measure which code statements have been executed during your E2E tests, the code needs to be instrumented (adding additional counters to your source code before running it).
This is accomplished with istanbul.js, so let's install it together with the libraries needed for istanbul to understand our TypeScript files:
npm i -D @jsdevtools/coverage-istanbul-loader @istanbuljs/nyc-config-typescript istanbul-lib-coverage nyc webpack
We can now configure istanbul to work with TypeScript by creating an istanbul configuration file .nycrc at the project root:
2. Adding Cypress code coverage and webpack configuration
We have to configure webpack to instrument the code when building our project, so we create a new file cypress/coverage.webpack.ts and add the following content:
Also, add “node” to the types array in cypress.tsconfig.json to avoid the type warning.
Finally, we can install the cypress code coverage library:
npm i -D @cypress/code-coverage
3. Configure Cypress
In cypress/support/e2e.ts, we import the code coverage library directly below import ‘./commands’ by adding this one-liner:
Now we can update cypress.config.ts by replacing the e2e object with the following:
On top of the file, we also need to import the function:
import * as registerCodeCoverageTasks from '@cypress/code-coverage/task';
4. Extending the build process
To extend the angular-cli build process, we install @angular-builders/custom-webpack:
npm i -D @angular-builders/custom-webpack
In angular.json, find the line “builder”: “@angular-devkit/build-angular:browser”, and replace it with:
Then, also in the angular.json, add the following additional build configuration in architect.build.configurations:
Instead of modifying the build process of our local server, we create a new ng serve command to instrument our codebase only when running E2E tests. To do so, add the following block in your angular.json file below the “serve” block (replace myproject with your project name as defined in the package.json):
Now, we replace the ng serve in the E2E section with our custom webpack configuration (replace myproject with your project name from the package.json file):
To have the commands handy, add them to the package.json “scripts” section right after the line “e2e” (replace myproject with your project name):
That’s it! We can now run our tests and view the coverage information (if you newly installed cypress and have no tests yet, remove the line cy.contains(‘Replace me with something relevant’); from integration/spec.ts):
npm run e2e:ci && npm run e2e:coverage
The console will show you the coverage percentage, when you open the index.html file inside coverage/lcov-report/, you can see a nice HTML report to inspect the E2E coverage of your application:
What now? You can now implement the coverage analysis in your CI setup (e.g. using CircleCI, Bitbucket Pipelines or Github Actions) and to connect it with your code quality inspection tool (e.g. SonarCloud).
Next up in the Angular DevOps series:
- Angular code quality inspection with SonarCloud [coming soon]
- Continuous Integration (CI) with Angular and Bitbucket Pipelines [coming soon]
This tutorial was respectfully inspired from these previously published articles:
21 December 2022
- Added a note on importing registerCodeCoverageTasks
- Reformatted the article to use code blocks
19 October 2022
- Updated the article for Cypress v10 and @cypress/schematic v2.2. It now follows the updated folder structure, given the introduction of component tests alongside the E2E tests treated in this article
6 August 2022
- Updated the example repository to Angular 14 and Cypress 10
- Fixed a crucially missing word action word in the sentence on avoiding type warnings
- Removed fixing the version of @angular-builders/custom-webpack, the underlying bug in @jsdevtools/coverage-istanbul-loader was resolved
23 December 2021
- Added Node v16 as prerequisite
13 November 2021
- Updated tutorial to use the official Angular Cypress schematic
- Removed the notes on Webpack ^5.0.0
- Updated the used dependencies to use better supported packages: @jsdevtools/coverage-istanbul-loader and @angular-builders/custom-webpack
- Removed the step of passing a custom webpack configuration to the cypress preprocessor
2 April 2021
- Added Note on Webpack ^5.0.0 to use a temporary cypress webpack preprocessor instead of @cypress/webpack-preprocessor
- Added Note on Webpack ^5.0.0 in step #2, on how to use a fork with a peer dependency on Webpack v5 of istanbul-instrumenter-loader.