title: React Testing - TypeError: baseReducer is not a function
body: <p>I'm having some issues with unit tests (RTL). It's really quite bizarre. My tests were running fine, but then I modified my store.js, and then my App.test.js started failing, the rest kept passing... And then if I modified a test, it would fail (even if it was a dumb component) with the same error (TypeError: baseReducer is not a function). So I tried replicating it in codesandbox but I can't? If you look at the example in the codesandbox, it's pretty close to the production app setup.</p>
  <p>So far I have tried:</p>
  <ol>
  <li>Returning the appReducer instead of the root Reducer</li>
  <li>Commenting out everything in the app reducer except 1 (tried each one)</li>
  <li>Returning fooReducer and barReducer instead of the actual feature reducers in the application.</li>
  </ol>
  <p><a href="https://codesandbox.io/s/react-help-basereducer-error-forked-p89dw" rel="nofollow noreferrer">https://codesandbox.io/s/react-help-basereducer-error-forked-p89dw</a></p>
  <p><em>The redux implementation works fine in browser</em></p>