Neither Test::Unit nor MiniTest rescue exceptions like Interrupt or
NoMemoryError, but ActiveSupport::Testing::SetupAndTeardown#run which
overrides MiniTest::Unit::TestCase#run rescues them.

Rescuing an Interrupt exception is annoying, because it means when you
are running a lot of tests e.g. when running one of the rake test tasks,
you cannot break out using ctrl-C.

Rescuing exceptions like NoMemoryError is foolish, because the most
sensible thing to happen is for the process to terminate as soon as
possible.

This solution probably needs some finessing e.g. I'm not clear whether
the assumption is that only MiniTest is supported. Also early versions
of MiniTest did not have this behaviour. However, hopefully it's a
start.

Integrating with Test::Unit & MiniTest has always been a pain. It would
be great if both of them provided sensible extension points for the kind
of things that both Rails and Mocha want to do.