Fail on unused dependencies in test package

[big-andy-coates]

Currently, if there are unused input or expectation files in a a test package a warning is logged. Unused files can be an indication that a test is incorrect, i.e. referencing the wrong input/expectation. At the very least, it's noise that can mislead the next person in there.

We should therefore make the default to fail the test execution, i.e. fail hard / fail fast. Then add an option to switch this to 'log warning' if that's what the user wants.