global

def aggregate_failures(*args, &block)

the same, so this is the best we can do.
`Minitest::Assertion`, but Minitest's implementation does not treat subclasses
It would be nice to make `MultipleExpectationsNotMetError` subclass
it gets counted in minitest's summary stats as a failure rather than an error.
Convert a `MultipleExpectationsNotMetError` to a `Minitest::Assertion` error so 
def aggregate_failures(*args, &block)
  super
rescue RSpec::Expectations::MultipleExpectationsNotMetError => e
  assertion_failed = Minitest::Assertion.new(e.message)
  assertion_failed.set_backtrace e.backtrace
  raise assertion_failed
end