Unit tests

[wfatherley]

This is a perpetual umbrella issue. Specific unit tests should be raised in their own issue and linked to this one (#2)

[wfatherley]

Upon closing this issue, all subsequent issues are to be closed only by pull request in most cases. Therefore, a PR should have changes to /tests that cover modifications of the library itself.

[wfatherley]

There are several unit/integrated tests for ExceptionFrom that are probably unnecessary and can be removed. There are still several core functions that need tests

[wfatherley]

Need to look into line number tests. They are currently commented out because they are internal unit tests that require a hook in the source, and the functional/e2e tests running now make them redundant.