new_contents: from unittest import TestCase
  
  from robber import expect
  from robber.bad_expectation import BadExpectation
  
  
  class TestBadExpectation(TestCase):
      def test_message(self):
          # The error message will show up as long as it is the string representation of the Exception.
          # So this simple test is enough.
          message = 'You did something wrong!'
          bad_expectation = BadExpectation(message)
          expect(str(bad_expectation)).to.eq(message)
  
subject: Add test for BadExpectation