Improve IR tests

The IR unit tests currently only check that errors were not thrown when building the `AirIR` from the parsed source. We should also ensure that the resulting IR is expected, and more rigorous testing should be added for edge cases

Look for IR unit tests in the codebase, likely in a test module or directory. Understand how AirIR is built from parsed source. Add assertions to verify the resulting IR structure matches expectations. Identify edge cases in the language specification and write additional tests for them.

Written by the indexing model from the issue text.