aquaregia_test: Better error message matching #9
Description
A major piece of debt in aquaregia_test (which verifies error messages for failing test cases)
is that it just searches for N instance of error X in the output.
We can do better: we should assert error messages at specific positions.
One way we could do this is how analysistest expects error messages: with // want comments next to where the errors are expected.
We should also move all the test cases to a testdata/ folder so we don't have to tag them with the failing constraint.