By Austin Bingham

Currently the most popular Jest test runner extension for VS Code is vscode-jest by Orta. For most common setups, this extension works without any configuration needed to VS Code. In my case, though, I needed to enable Node's support for ECMAScript modules. The Jest documentation lists a few ways to do this, and I decided to use the the method that involves setting an environment variable.

Because I needed to set this environment variable, vscode-jest's default behavior didn't work, and I ended up needing to create a run configuration. This was not particularly complicated, but it was complicated enough that I thought I should capture the knowledge here.

Configuring the Jest command

First you need to configure the Jest command in your settings. To do this you can use the extension's "Setup Extension" command. From the command palette, run "Jest: Setup Extension" (or possibly "Jest: Setup Extension (beta)" if it's still in beta). Choose "Setup Jest Command" in the dropdown this produces.

It will ask if you can run Jest tests from the terminal; choose "yes". When it then asks for the Jest command line, enter "NODE_OPTIONS=--experimental-vm-modules node_modules/.bin/jest".

This will add an entry like this to your settings.json:

"jest.jestCommandLine": "NODE_OPTIONS=--experimental-vm-modules node_modules/.bin/jest"

The "NODE_OPTIONS=..." enables ECMAScript modules in node. Enabling support for modules in jest.jestCommandLine seems to be necessary for VSCode's testing framework to discover tests. However, this bit of configuration is not sufficient for running and debugging tests. For that, we need to create a launch configuration.

Creating the launch configuration

You'll then return to the setup wizard's dropdown list. This time select "Setup Jest Debug Config", and then select "Generate". This will add a run configuration to your launch.json. Now you can select "Exit" from the wizard.

Now that you have the launch configuration, you need to edit it to add the environment variable. Add this to the launch configuration inside launch.json:

"env": {
    "NODE_OPTIONS": "--experimental-vm-modules"
}

You should end up with a configuration that looks something like this:

{
    "configurations": [
        {
            "type": "node",
            "name": "vscode-jest-tests",
            "request": "launch",
            "console": "integratedTerminal",
            "internalConsoleOptions": "neverOpen",
            "disableOptimisticBPs": true,
            "program": "${workspaceFolder}/node_modules/.bin/jest",
            "cwd": "${workspaceFolder}",
            "args": [
                "--runInBand",
                "--watchAll=false"
            ],
            "env": {
                "NODE_OPTIONS": "--experimental-vm-modules"
            }
        }
    ]
}

With this in place, you should be able to run and debug Jest tests from the test tool or directly from the test file.

Category: misc
Tags: Node, Jest, Testing