[BUGFIX beta] Add spec for unhandled exception being logged by Test.adapter.exception

The changes in exception handling introduced in
cf0caa04f625067ec3b4629acdec12c8517df94e made a test assertion in an
existing test obsolete, since it wasn't called anymore.

This commit adds a spec for Test.adapter.exception being invoked, when
an exception is not handled.
Merge pull request #3705 from pangratz/fix/spec_for_unhandled_exception

[BUGFIX beta] Add spec for unhandled exception being logged by Test.adapter.exception