The optimal flow for Jest based testing in VS Code
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README.md

vscode-jest Build Status


Content


The Aim

A comprehensive experience when using Facebook's Jest within a project.

  • Useful IDE based Feedback
  • Session based test watching

Screenshot of the tool

Maintainers

Orta Therox (@orta), Sean Poulter (@seanpoulter), Vincent Voyer (@vvo) & ConnectDotz (@connectdotz).

Features

  • Starts Jest automatically when you're in a root folder project with Jest installed.
  • Show individual fail / passes inline.
  • Show fails inside the problem inspector.
  • Highlights the errors next to the expect functions.
  • Adds syntax highlighting to snapshot files.
  • A one button update for failed snapshots.
  • Show coverage information in files being tested. (requires coverage to be collected by your jest config)

How to get it?

Open up VS Code, go search for the extension "Jest".

How to get it set up?

This project has the expectation that you would run something like npm run test which just looks like jest in the package.json. So, please keep your configuration inside the package.json as opposed to using command line arguments.

If have a more complex setup, it can probably be supported, check out the settings. They are all prefixed with jest.

Also, you should use Jest 17+, however 16 works - it will just offer a warning. We're aiming to try and do current Jest version - 1, but won't specifically drop support for older versions unless we're forced into it.

How do we start the Jest?

The extension will start Jest for you when:

  • we find Jest configuration files in the workspace: jest.config.js or jest.json
  • we find Jest installed in the workspace: node_modules/.bin/jest
  • we find the workspace has been bootstrapped with create-react-app: node_modules/react-scripts/node_modules/.bin/jest
    • node_modules/react-native-scripts
  • you run the Jest: Start Runner command

How do I debug tests?

The simplest use cases should be supported out-of-the-box, but at the latest when VS Code displays errors about the attribute program or runtimeExecutable not being available, you have to create your own debug configuration within launch.json.

This plugin provides blueprints for debugging plain Jest setups or projects bootstrapped by create-react-app. (In the latter case you may have to edit the runtimeExecutable to reflect the used react-scripts package.) If those don't match your setup, you can modify the blueprints or create a completely new debug configuration, but keep in mind, that the type has to be node and that the configuration has to be named "vscode-jest-tests". In order to learn more about debug/launch configurations in general, visit VS Code Docs: Debugging.

Starting with debugging is possible by clicking on the debug CodeLense above appendant it tests, but you can also debug all tests at once by starting debugging of "vscode-jest-tests" within the VS Code Debug Side Bar.

Notes for troubleshooting

In contrast to previous versions of this plugin the debug settings are now independent from VS Code's jest.pathToJest and jest.pathToConfig setting. If you had to modify one of these, you pretty surely have to create a custom debug configuration and modify its path. This especially includes cases, in which jest isn't at its default location.

How do I show code coverage?

To show code coverage in the VS Code, you will need to:

  • Configure Jest to collect coverage information using the config or command line options
  • Show the coverage overlay:
    • Run the Jest: Toggle Coverage Overlay command to show the overlay once
    • To configure the extension to show the coverage overlay when your workspace loads, add the following setting:
      {
          "jest.showCoverageOnLoad": true
      }

Inspiration

I'd like to give a shout out to Wallaby.js, which is a significantly more comprehensive and covers a lot more editors, if this extension interests you - check out that too.

Wanted

Someone to take responsibility for ensuring that the default setup for create-react-app is always working. All the current authors use TypeScript and React/React Native and so have very little familiarity with changes to CRA. Apply via PRs :D.

Troubleshooting

start jest from non-root folder

If you don't use the root of your project for your JS with Jest tests, do not worry, you can still use this project. You will need to use the "Start Jest Runner" command, and maybe have to configure your own jest.pathToJest setting inside the .vscode/settings.json to whatever you would use.

These are the activation events which trigger the runner to start:

  "activationEvents": [
    "workspaceContains:node_modules/.bin/jest",
    "workspaceContains:node_modules/react-scripts/node_modules/.bin/jest",
    "workspaceContains:node_modules/react-native-scripts",
    "onCommand:io.orta.jest.start"
  ],

These are the things that will trigger the extension loading. If one of these applies, and you're not seeing the "Jest" in the bottom bar, reference the self-diagnosis below

non-standard environments

vscode-jest supports common jest configuration, such as when jest is in root/node_modules/.bin/jest, or for react-native root/node_modules/react-native-scripts.

However, if your repo doesn't fall into these patterns or you want to pass extra parameters, you can easily use the jest.pathToJest or jest.pathToConfig settings to instruct the plugin on how to start jest. You can even use the scripts from package.json, such as npm run test -- or yarn test. Feel free to experiment and search the issues for many examples.

plugin not running as expect? try self-diagnosis

If your can execute jest tests on command line but vscode-jest was not running as expected, here is what you can do to find out what it is actually doing:

  1. click on Jest:stopped on status bar to show Jest Output window: Screenshot of the tool
  2. turn on the debug mode: set "jest.debugMode": true in .vscode/settings.json
  3. restart vscode-jest or reload the window (via Reload Window command)
  4. open the developer tool (via Help > Toggle Developer Tools menu), you should see more information including how we extract jest config and spawn jest processes.

Hopefully most issues would be pretty obvious after seeing these extra output, and you can probably fix most yourself by customizing the jest.pathToJest and other settings.

Want to Contribute?

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