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Contributing to Create React App's E2E tests

This is an end to end kitchensink test suite, but has multiple usages in it.

Running the test suite

Tests are automatically run by the CI tools.
In order to run them locally, without having to manually install and configure everything, the yarn e2e:docker CLI command can be used.

This is a simple script that runs a Docker container, where the node version, git branch to clone, test suite, and whether to run it with yarn or npm can be chosen.
Simply run yarn e2e:docker -- --help to get additional info.

If you need guidance installing Docker, you should follow their official docs.

Writing tests

Each time a new feature is added, it is advised to add at least one test covering it.

Features are categorized by their scope:

  • env, all those which deal with environment variables (e.g. NODE_PATH)

  • syntax, all those which showcase a single EcmaScript syntax feature that is expected to be transpiled by Babel

  • webpack, all those which make use of webpack settings, loaders or plugins

Using it as Unit Tests

In it's most basic for this serve as a collection of unit tests on a single functionality.

Unit tests are written in a src/features/**/*.test.js file located in the same folder as the feature they test, and usually consist of a simple ReactDOM.render call.

These tests are run by jest and the environment is test, so that it resembles how a Create React App application is tested.

Using it as Integration Tests

This suite tests how the single features as before behave while development and in production.
A local HTTP server is started, then every single feature is loaded, one by one, to be tested.

Test are written in integration/{env|syntax|webpack}.test.js, depending on their scope.

For every test case added there is just a little chore to do:

  • a case statement must be added in src/App.js, which simply perform a dynamic import() of the feature

  • add a test case in the appropriate integration test file, which calls and awaits initDOM with the previous SwitchCase string

An usual flow for the test itself is something similar to:

  • add an id attribute in a target HTML tag in the feature itself

  • since initDOM returns a Document element, the previous id attribute is used to target the feature's DOM and expect accordingly

These tests are run by mocha (why not jest? See this issue) and the environments used are both development and production.