mobx 5.0.0-beta.6 gives "TypeError: allKeys[x].match is not a function" when testing TS Array with Jest

[tkivela]

I have a small template project with Mobx 4.2 / Typescript which works fine, including testing store with Jest.

I updated Mobx dependency to 5.0.0-beta.6 and the code seems to work otherwise fine but testing the store gives an error "TypeError: allKeys[x].match is not a function". The row which fails just tests TypeScript Array equality to [].

Output when running 'yarn' and then 'yarn test':
FAIL src/stores/app/index.test.ts
● AppStore › addCounterNote should add new note to notes array beginning

TypeError: allKeys[x].match is not a function

   6 | 
   7 |     expect(store.counter).toEqual(0)
>  8 |     expect(store.notes).toEqual([])
   9 |     store.addCounterNote()
  10 |     expect(store.counter).toEqual(1)
  11 |     expect(store.notes.length).toEqual(1)
  
  at Object.<anonymous> (src/stores/app/index.test.ts:8:25)

A repository which reproduces the problem can be found at https://github.com/tkivela/react-ts-mobx-template-v5jestproblem

I'm not sure if this is a Mobx problem but the fact that same works with Mobx 4.2 implies that the problem could atleast be a compatibility issue which should be documented somewhere in v5 docs.

[mweststrate]

This is a bug in Jest, see: jestjs/jest#6391

[tkivela]

Ok, thanks @mweststrate , nice find! I hope they merge your PR to Jest soon. I'll close this for now as the problem was not actually in Mobx.