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Desktop Front-end testing

In order to make testing easier we created some helpers that can be accessed by including

const { ExperimentFakes } = ChromeUtils.import(

Testing your feature integrating with Nimbus#

You need to provide a feature configuration and await enrollment

let doEnrollmentCleanup = await ExperimentFakes.enrollWithFeatureConfig({
featureId: "<YOUR FEATURE>",
// You can add values for each variable you added to the manifest
value: {
enabled: true
// Now you can assume the feature is enabled so you can
// test and that it's doing the right thing
// Assert.ok(It works!)
// Finishing up
await doExperimentCleanup();

Testing with a live Nimbus recipe#

If you already published an experiment through Nimbus then you will want to test enrollment in the browser.

  1. Flip the following pref to true in the browser you want to enroll (in about:config)


  1. You need to copy paste the following URL and fill in the required details.

For experiments that are already live:


For experiments that are in "preview" mode:


Testing with Desktop Rollouts#

For writing tests you usually want to have the following modules imported:

const { ExperimentAPI, NimbusFeatures } = ChromeUtils.import(
const { ExperimentFakes } = ChromeUtils.import(

Next this is how you would set up your feature to test integration with Desktop Rollouts:

// Ensure everything has finished initializing
await ExperimentAPI.ready();
// The actual setup
await ExperimentFakes.remoteDefaultsHelper({
// Reference your feature already defined in the FeatureManifest.js
feature: NimbusFeatures.<YOUR FEATURE>,
configuration: {
// An identifier used in telemetry
slug: "my-test-configuration",
// Is the feature on or off
enabled: true,
// Any additional variables
variables: {},
// Now your feature integration is ready for testing
// NimbusFeature.<YOUR FEATURE>.isEnabled()
// NimbusFeature.<YOUR FEATURE>.getAllVariables()