[Bug Report] Using @vue/test-utils in sync mode leads to test failures

[kierans]

Environment

Vuetify Version: 2.2.12
Vue Version: 2.6.10

Steps to reproduce

1. Create a new project via Vue CLI
2. Ensure that the version of @vue/test-utils < 1.0.0-beta.30
3. Write a set of unit tests that exercise form validation

Expected behaviour

npm run test:unit runs successfully.

Actual behaviour

npm run test:unit tests will fail with TypeError: Cannot read property '$scopedSlots' of undefined error message.

[kierans]

As outlined in vuejs/vue-test-utils#1137 the reason is due to @vue/test-utils running in sync mode which doesn't work well with how Vue updates the DOM in a batch.

When adding Vuetify to a project via the CLI, I suggest that any entry of @vue/test-utils be upgraded to >= 1.0.0-beta.30 so that sync mode is no longer present. This will have the consequence of forcing unit tests to await DOM updates.

[KaelWD]

Duplicate of vuetifyjs/vuetify#9151

I suggest that any entry of @vue/test-utils be upgraded to >= 1.0.0-beta.30

This would break any existing tests, the upgrade should be done manually if needed.

[kierans]

This would break any existing tests, the upgrade should be done manually if needed.

But it is likely that tests (at least those using mount) will break anyway because sync mode doesn't work well with Vuetify.

The plugin could output a warning message, or ask the user if they want to upgrade @vue/test-utils.