add more tests

[dlyongemallo]

The test coverage is quite limited right now, and it would be good to add more tests.

In particular, when more functionality is added, tests help both to ensure that regressions or new bugs don't happen and to make it easier for someone reading the code to understand what it is intended to do and to document edge cases or unimplemented features.

A lot of new features were added recently which I'm trying to understand and it would be very helpful to me to see, e.g., what the intended inputs and expected outputs are for typical use cases. (Maybe the inputs/outputs are obvious to someone more versed in ZX-calculus, but I'm still learning.)