unit tests and image preloading

[noah10]

I coded up a face-name experiment and wrote some unit tests for it. Everything worked great, but it lacked image preloading. Once I added it, my unit tests broke because image preloading appears to halt the timeline in the jest environment. Whenever I examine getDisplayElement().innerHTML it's always a progress bar.

I've tried the following variations on mocking/stubbing image preloading:

jsPsych.pluginAPI.preloadImages = jest.fn((x, cb) => { cb(); }); // taken from the jsPsych preload unit test
jsPsych.pluginAPI.preloadImages = jest.fn();
jsPsych.pluginAPI.preloadImages = () => {};
jest.spyOn(jsPsych.pluginAPI, "preloadImages").mockImplementation(() => null);

...all to no avail. All of these attempts happen in my beforeEach block before I call jsPsych.init:

beforeEach(() => {
        jsPsych.pluginAPI.preloadImages = jest.fn((x, cb) => { cb(); });
        jsPsych.init({
            timeline: (new FaceName(1)).getTimeline(),
        });
        expect(jsPsych.pluginAPI.preloadImages).toHaveBeenCalled();
        jest.useFakeTimers("legacy");
    });

Any suggestions on what I can do to essentially ignore image preloading in my test environment? Unless anyone has any other ideas I'll probably just modify the timeline in my test env to get rid of the preload step, though that doesn't seem ideal.