getRoot in afterAttach returns undefined in Jest tests

Bug report

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• I've made sure my project is based on the latest MST version
• Fork this code sandbox or another minimal reproduction.

Sandbox link or minimal reproduction code https://codesandbox.io/s/mobx-state-tree-todolist-wvupz?file=/index.test.js

Describe the expected behavior getRoot(self) should be defined in afterAttach

Describe the observed behavior It is undefined