old_contents: from unittest import TestCase
  
  
  class TestBuildError(TestCase):
      def test_push_message(self):
          self.fail()
  
      def test_format_as_single_string(self):
          self.faildoo()
  
new_contents: from unittest import TestCase
  
  from builderror import BuildError
  
  class TestBuildError(TestCase):
  
      def test_that_multiple_pushed_messages_are_formatted_properly_when_asked_for(self):
          err = BuildError()
          err.push_message('message about error details')
          err.push_message('message about error context')
          formatted_message = err.format_as_single_string()
          self.assertEquals(formatted_message, 'message about error context\nmessage about error details')
  
  
subject: Put in first proper tiny package class and unit test.