Proposal: Allow context to teardown and setup repeatedly in a test

[mixonic]

The goal

I maintain a suite of tests that use a helper simulatePageRefresh to destroy the currently running application, then instantiate a new one. The implementation, compatible until ember-qunit 4 (and possibly 5), looks like this:

export async function simulatePageRefresh() {
  let context = getContext();

  await teardownContext(context);
  await setupContext(context);
  await setupApplicationContext(context);
}

This helper allows us to assert, in application tests, that a fresh page load (from Ember's perspective) performs data loading correctly (either from mocked APIs or from real APIs).

This functionality is not a robust as a true page reload, such as we would get from writing these tests in Playwright. However, as we already have these tests in Ember-QUnit and Ember-QUnit already embraces booting an application multiple times in the same browsing context, this functionality doesn't seem bizarre.

Why our implementation no longer works

In ember-qunit, setupContext and teardownContext define how a testing context is configured and reset. See https://github.com/emberjs/ember-qunit/blob/dafee6bdb9a93ab6a83de7421adad6669df31d95/addon/src/index.js#L51

setupContext, at

ember-test-helpers/addon/addon-test-support/@ember/test-helpers/setup-context.ts

Line 382 in 9cec68d

export default function setupContext<T extends object>(

uses the QUnit test context (passed here) as a key for destructors and even adds the context into the destroyable tree (associated with the Ember owner instance) at

ember-test-helpers/addon/addon-test-support/@ember/test-helpers/setup-context.ts

Line 425 in 9cec68d

associateDestroyableChild(context, owner);

.

Although teardownContext calls destroy with the context at

ember-test-helpers/addon/addon-test-support/@ember/test-helpers/teardown-context.ts

Line 25 in 9cec68d

export default function teardownContext(

, this does not prevent the context from being tracked as "destroyed". That state then makes it impossible to call setupContext a second time, as the destructible codepaths complain the instance was already destroyed.

Proposal for discussion

I think there are several ways forward:

• We can restore using teardownContext and setupContext multiple times in a test as a functionality of this library
  • We could attempt to make sure teardownContext somehow disconnects the destructible or destroyed status tracking, leaving the testing context clean for re-use.
  • We could add a new object on the testing context which is added by setupContext and provides the destructible target, and remove that from the context on teardownContext.
• We optionally also, or perhaps alternatively, introduce a first class helper for "restart the application"
• In either case, tests would be added to ensure the proposed functionality continues to work going forward.

This issue is to gather feedback from others and ideally gain some consensus before we do the technical implementation.

cc @eliasdawson-addepar @NullVoxPopuli @IgnaceMaes

[NullVoxPopuli]

I think if this library can figure out any way to simulate a refresh, that's fantastic, and I'd be very happy to see such a feature -- I've implemented something like what you have at a prior employer, and it was a good tool.

I don't think it makes too much sense to have a first-class helper for "restarting the application" yet, because it could require figuring out how to clean up DOM body/head/etc. Since test-helpers renders things into the test container, via ember-qunit, I think simulating a refresh is much safer in library land.