The previous approach did avoid a fair number of jest.mock calls, but
made debugging the tests harder. If you don't know about the mapping
it's unclear why the imported module does not behave as normal.
By forcing the use of jest.mock it means that the answer to that
question is in the test you are working on.
react-calendar-heatmap's output depends on the timezone, which means
that snapshots can fail if the timezone changes. This sets the timezone
as UTC during client tests to avoid that problem.
