Check tests for validation

[JoeZiminski]

    key = next((key for key in datetime_keys if f"_{key}-" in name), None)

There was a bug in the (pre-existing) code! It will be true when searching for date if there is a datetime flag. Wrapping in _{key}- should stop this from happening.

Originally posted by @JoeZiminski in #510 (comment)

There was a bug caught here in the existing codebase that tests did not catch. Review tests to understand why this was missed + add tests for similar cases.

[JoeZiminski]

So the full code was:

    formats = {
        "datetime": "%Y%m%dT%H%M%S",
        "time": "%H%M%S",
        "date": "%Y%m%d",
    }

    key = next((key for key in formats if key in name), None)

It was properly tested and behaving as expected, because "datetime" is before "date" in the format dictionary, and so was always checked first. If the bug was exposed (e.g. "date" before "datetime") then the test would fail. Added protection is added in #510 but this is not a cause for concern here - the test coverage is good.