Bug: Possible memory leak when using real Vuex store in plugins

[rappjt]

Describe the bug

I have a project with 8,000+ tests using mocha, many of which create a real Vuex store. Recently we have migrated to Vue3 and test-utils v2. After the upgrade a memory leak is causing the test suite to fail as it runs out of heap space. At this time it seems to be adding a plugin (store) when mounting causes the issue, though not fully sure if there is additional cleanup I must be doing that isn't mentioned in docs.

To Reproduce

I have created the HelloWorld project from vue-cli (webpack, vuex, mocha), and modified the one and only test in that project:

1. Looped single test many times
2. created a store and added to global.plugins for each test
   1. I used this example to create/add the store

describe('HelloWorld.vue', () => {
  for (let i = 0; i < 10000; i++) {
    it(`${i}`, () => {
      const store = createStore({
        state () {
          return {
            count: 0
          }
        },
        mutations: {
          increment (state) {
            state.count += 1
          }
        }
      })

      const msg = 'new message'
      const wrapper = shallowMount(HelloWorld, {
        props: { msg },
        global: {
          plugins: [store]
        }
      })
      expect(wrapper.text()).to.include(msg)
    })
  }
})

When I inspect this while running I can observe each test is leaking memory. Simply, not creating store and not pass in plugins, I no longer see the leak.

Expected behavior

Run entire test suite without getting out of heap exception.

Related information:

• @vue/test-utils version: 2.1.0
• Vue version: 3.2.39
• node version: 14.18.1 and 16.17.1
• vuex version 4.0.2
• @vue/cli-plugin-* version ~4.5.19

Additional context

A few other things I have tested:

• creating one store for all tests and setting with config.global.plugins = [store], still saw leak
• created store but did not actually use in config.global.plugins or in shallowMount, did not see leak

[cexbrayat]

@rappjt Thanks for raising this issue. Would you mind pushing your repro to a GitHub repo so someone can take an easy look?

[freakzlike]

Can you also try again with wrapper.unmount() or enableAutoUnmount? Maybe this makes a difference

[rappjt]

@cexbrayat - Thank you for the quick response, here is a repo I hope will demonstrate the issue https://github.com/rappjt/vuejs-test-utils-plugin-vuex-memory-issue

@freakzlike - Thanks for the suggestion, in my original project I am doing this and still see the issue. I didn't show this in original post as I was trying to make minimal changes to the original test from vue-cli. However, I added unmount in repo listed above and still see the issue

[freakzlike]

I was able to reproduce it within VTU tests and I could break it down to:

test-utils/src/vueWrapper.ts

Line 125 in 5c1dceb

private attachNativeEventListener(): void {

The changes in #1793 have reduced the memory in my test case from ~700 MB to ~300 MB so there is still some more optimization needed