Add jest tests for React components

Add a Jest test to `Main.test.tsx` that renders the Main component, fills out the transition form, and renders the results table using the FakeApi. This tests interactions with the form and the container logic. Use [react testing library](https://testing-library.com/docs/react-testing-library/example-intro) and [user-event](https://testing-library.com/docs/ecosystem-user-event) to render and interact with the page. [Here](https://github.com/alexjball/rate-quote/blob/master/src/App.test.js#L19) is an example of a Jest test that renders and fills out another form.