title: MobX makeObservable does not work with Jest
body: <p>I am trying to test my stores with Jest and when I use makeObservable, I get the following error:</p>
  <pre><code>[MobX] Cannot apply 'observable' to 'TodoStore@3.todos': Field not found.
  
        23 |
        24 |   constructor() {
      &gt; 25 |     makeObservable(this, {
           |                   ^
        26 |       todos: observable,
        27 |       filter: observable
        28 |     })
  
        at die (node_modules/mobx/src/errors.ts:84:15)
        at ObservableObjectAdministration.make_ (node_modules/mobx/src/types/observableobject.ts:250:17)
        at forEach (node_modules/mobx/src/api/makeObservable.ts:37:49)
            at Array.forEach (&lt;anonymous&gt;)
        at makeObservable (node_modules/mobx/src/api/makeObservable.ts:37:30)
        at new TodoStore (src/typings/models/ToDoStore.ts:25:19)
        at tests/looseReplaceNodes.test.ts:76:17
        at step (tests/looseReplaceNodes.test.ts:33:23)
        at Object.next (tests/looseReplaceNodes.test.ts:14:53)
        at tests/looseReplaceNodes.test.ts:8:71
  </code></pre>
  <p>Class in question:</p>
  <pre><code>export class TodoStore {
    todos: Todo[]
    filter: string
  
    constructor() {
      makeObservable(this, {
        todos: observable,
        filter: observable
      })
      this.todos = []
      this.filter = &quot;&quot;
    }
    createTodo(value: any) {
      this.todos.push(new Todo(value))
    }
  }
  </code></pre>
  <p>This goes away when I use makeAutoObservable instead but that doesn't work for my use-case (this is a toy example). I don't want to use decorators as MobX seems to be moving away from this.</p>
  <p>Any ideas?</p>