Support cleaning up wrappers automagically

What problem does this feature solve?

Currently it is necessary to call wrapper.destroy() / wrapper.vm.$destroy() manually. Forgetting to do so may result in difficult to track down side effects and performance degradation (especially when not mocking Vuex).

What does the proposed API look like?

Introduce a new enableAutoDestroy() helper which accepts a hook function such as afterEach() to call wrapper.destroy() as callback.

[winniehell]

@eddyerburgh I am interested in implementing this. Would you accept a pull request? 😃

[eddyerburgh]

Yep 😄

[winniehell]

As I realized from @souldzin's comment on the pull request (#1240 (comment)), the API proposed here does not work. For a hook like afterEach we want to make sure it is only called exactly once. I'm not sure how we would ensure that when passing it as an config option.

Instead we could provide an enableAutoDestroy() function that accepts the hook function as parameter. We could then rely on that function being called only once (in test setup).

[winniehell]

I have updated the description now with the new suggested API and will create a new pull request tomorrow.