refactor IR tests

[grjte]

This PR includes a trivial clippy fix and a quick refactor to split the IR tests into modules to make them more manageable and easier to update later. This addresses #138

[tohrnii]

Thank you @grjte, looks good to me. One question is if we should replace boundary_constraints and integrity_constraints in function names to their abbreviated forms (bc and ic) to be consistent except for boundary_constraints() and integrity_constraints()? If you agree with this change maybe it can be done with this PR?

[grjte]

Thank you @grjte, looks good to me. One question is if we should replace boundary_constraints and integrity_constraints in function names to their abbreviated forms (bc and ic) to be consistent except for boundary_constraints() and integrity_constraints()? If you agree with this change maybe it can be done with this PR?

Do you mean the accessor functions? I would probably leave them as it is and keep this PR as a tests refactor

[tohrnii]

No I actually meant just for test names. For eg, renaming boundary_constraints_with_constants to bc_with_constants etc.

[grjte]

No I actually meant just for test names. For eg, renaming boundary_constraints_with_constants to bc_with_constants etc.

Ah, I see. The way I had done it was to shorten it in the error case and leave it unshortened for the main test, but I don't feel strongly. I've changed it in all cases except when there's nothing else in the name (e.g. boundary_constraints)