Add more testing for `ComposedSchedule`

[darsnack]

ComposedSchedule is only implicitly tested through the cyclic schedules. This probably leaves out edge cases.

[a-cakir]

I would not mind taking a crack at this, however, I will probably need some handholding as I am relatively new to the Julia world.

[darsnack]

Thanks! Feel free to submit a PR even if it isn't complete, and I'd be happy to help guide it.