addLocalDurationClip and co don't have any tests

[phadej]

Changelog reads

add [add/diff][UTC/Local]Duration[Clip/Rollover]

but I don't see any tests for these functions. Arguably they are simple, but it would be nice to have at least one example for each in tests

• testing that they exist
• showing an example of their (clip/rollover) differences.

[phadej]

Ditto an addition of diffTimeOfDay

[AshleyYakeley]

Are they broken? Generally I add tests for things I don't have confidence in.

[phadej]

Are they broken?

Maybe there's a typo. I don't know.

My point is that if they are changed&removed or something else "breaking" is done to them, the current test suite has no chance highlighting that.