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Guide.Jest
Jest

Disclaimer

  • This guide describes installing Detox with Jest on a fresh project. If you're migrating an existing project, please apply some common sense in the process.

  • The guide has been officially tested only with Jest 24.x.x. We cannot guarantee that everything would work with other versions.

Installation

0. Set up Detox' fundamentals

Before starting out with Jest, please be sure to go over the fundamentals of the Getting Started guide.

1. Install Jest

npm install --save-dev jest

2. Set up test-code scaffolds

Run an automated init script:

detox init -r jest

Errors occurring in the process may appear in red.

Fix & Verify

Even if detox init goes well and everything is green, we recommend going over some fundamental things, using our homebrewed demo-react-native-jest example project as a reference.

a. Fix/verify this list of JSON properties:
File Property Value Description
package.json detox.test-runner "jest" Required. Should be "jest" for the proper detox test CLI functioning.
detox.runner-config (optional path to Jest config file) Optional. This field tells detox test CLI where to look for Jest's config file. If omitted, the path defaults to "e2e/config.json" (a file generated by detox init -r jest).
e2e/config.json testEnvironment "node" Required. Needed for the proper functioning of Jest and Detox.
setupFilesAfterEnv ["./init.js"] Required. Indicates which files to run before each test suite. The field was introduced in Jest 24.
reporters ["detox/runners/
jest/streamlineReporter"]		 Optional. Available since Detox 12.7.0. Sets up our highly recommended streamline-reporter Jest reporter, tailored for running end-to-end tests in Jest - which in itself was mostly intended for running unit tests. For more details, see the migration guide.
verbose true Must be true if you have replaced Jest's default reporter with Detox's streamlineReporter. Optional otherwise.

A typical detox configuration in a package.jsonfile:

package.json

b. Fix/verify the custom Jest init script (i.e. e2e/init.js):
  • beforeAll(), beforeEach(), afterAll() should be registered as hooks for invoking detox and/or a custom adapter.
  • The custom Detox-Jest adapter must be registered as a jasmine reporter (jasmine.getEnv().addReporter()). It is required for the artifacts subsystem to properly work.
  • (Recommended) Starting Detox 12.7.0, an additional, custom spec-reporter should be registered as a jasmine reporter, as well. This one takes care of logging on a per-spec basis (i.e. when it's start and end) — which Jest does not do by default. Should be used in conjunction with the Detox-Jest adapter.

A typical Jest log output, having set up streamline-reporter in config.json and spec-reporter in init.js:

Streamlined output

Writing Tests

There are some things you should notice:

  • Don't worry about mocks being used, Detox works on the compiled version of your app.
  • Detox exposes it's primitives (expect, device, ...) globally, it will override Jest's global expect object.

Parallel Test Execution

Through Detox' cli, Jest can be started with multiple workers that run tests simultaneously. In this mode, Jest effectively assigns one worker per each test file (invoking Jasmine over it). In this mode, the per-spec logging offered by the spec-reporter mentioned earlier, does not necessarily make sense, as the workers' outputs get mixed up.

By default, we disable spec-reporter in a multi-workers environment. If you wish to force-enable it nonetheless, the --jest-report-specs CLI option can be used.

How to run unit test and E2E tests in the same project

  • If you have a setup file for the unit tests pass ./jest/setup implementation into your unit setup.
  • Call your E2E tests using detox-cli: detox test