Closes #3663: add Filter Tests

[struppinet]

Amends: #3680

added the wished Filter Tests

[DanSheps]

1. Build is failing
2. No open issue, what is this currently fixing?

[struppinet]

lampwins wished for tests for this (#3680) so I added them.

[jeremystretch]

I've tweaked this to indicate that it amends the work contributed under #3680. Please also see my feedback above.

[struppinet]

Feedback has been applied. (tried save and failed on the automatic updated last_updated. didn't know about the update() method)

[jeremystretch]

didn't know about the update() method)

You generally want to avoid using update() as it bypasses most validation, but it can be very helpful in niche cases like this.