More informative exception handling in utils.tap

Currently it seems that the code raises ``Exceptions`` with the message ``'ERROR'`` and then then tests only go for a bare exception catches with try/except. I'm weeding out the latter cases, but ideally it would be great to have something more informative raised at the first place.

Start by locating the utils.tap implementation and the tests that currently raise exceptions with 'ERROR' or use bare try/except catches. Trace the existing exception paths and determine which informative errors and test expectations are needed; done means the relevant catches no longer hide the failure context and the updated tests pass.

Written by the indexing model from the issue text.