Testing: Add tests for new redux code with react-testing-library

[Alex-Cannon]

Depends on #64

We should test our new redux code to make sure it functions correctly. For example, we should test that the homepage, categories, orgs, etc. render correctly.

Basically, this ticket should be accepted when...

1. React-Testing-Library is added.
2. Testing file structure is decided.
3. We've tested the core functionality of new redux code