Previously we were patching ember-cli so that it would split the test bundle into two halves: the helpers, and the tests themselves. This was done so that we could use the helpers for `/theme-qunit` without needing to load all the core tests. This patch has proven problematic to maintain, and will become even harder under Embroider.
This commit removes the patch, so that ember-cli goes back to generating a single `tests.js` bundle. This means that core test definitions will now be included in the bundle when using `/theme-qunit`, and so this commit also updates our test module filter to exclude them from the run. This is the same way that we handle plugin tests on the regular `/tests` route, and is fully supported by qunit.
For now, this keeps `/theme-qunit` working in both development and production environments. However, we are very likely to drop support in production as part of the move to Embroider.
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