The screenenumeration-helpers.js requires an implementation of the ScreenEnumerationTest interfaces, which should emulate screen enumeration backends.

The ScreenEnumerationTest interface is defined as:

 class ScreenEnumerationTestChromium { initialize(); // Sets up the testing environment. async reset(); // Frees the resources. getMockScreenEnumeration(); // Returns `MockScreenEnumeration` interface. }; class MockScreenEnumeration { reset(); Empties data of created mock displays. setId(internalId, primaryId); // Set primary screen and internal screen IDs. setSuccess(success); // Set boolean to validate getDisplays() returned values. addDisplay(display); // Push display to the display vector. async getDisplays(); // Interceptor of getDisplays (screen_enumeration.mojom). }; 

Other helper-functions are located in screenenumeration-helpers.js

makeDisplay(id, bounds, work_area, scale_factor); // Create display object. 

The Chromium implementation of the ScreenEnumerationTest interface is located in mock-screenenumeration.js.

Other browser vendors should provide their own implementations of the ScreenEnumerationTest interfaces.