testing the testing framework :)

my goal is to test the normal cases and the edge cases

ex: isMultiDay - test one expecting true, one expecting false, and one with invalid input (so false)

As discovered in e-mission#1033 (comment), this function was not working as expected - it formats a key for lookup, and then didn't actually use the key.
With this fix, the test runs correctly!

continuing to improve testing coverage for diaryHelper by adding tests for more functions

For some of the functions related to a trip, I found it easiest to look at a trip in the logs, create a test trip object with the relevant parts, and then also mock the results

We should only look for tests in our `www/__tests__` directory, not any other `__tests__` directories that may exist in dependencies or anywhere in the project directory tree.
Further, by explicitly ignoring these directories, we don't have to specify `npx jest www/__tests__`, and can simply run `npx jest`.