new_contents: from unittest.mock import Mock, call
  
  from baby_steps import given, then, when
  from pytest import raises
  
  from district42 import Schema, schema
  
  
  def test_non_implemented_invert():
      with when, raises(Exception) as exception:
          schema.str.__invert__()
  
      with then:
          assert exception.type is AttributeError
  
  
  def test_non_implemented_mod():
      with when, raises(Exception) as exception:
          schema.str.__mod__(None)
  
      with then:
          assert exception.type is AttributeError
  
  
  def test_override_invert():
      with given:
          mock_ = Mock()
          Schema.__override__("__invert__", mock_)
  
      with when:
          schema.str.__invert__()
  
      with then:
          assert mock_.mock_calls == [call()]
  
  
  def test_override_mod():
      with given:
          mock_ = Mock()
          Schema.__override__("__mod__", mock_)
  
      with when:
          schema.str.__mod__()
  
      with then:
          assert mock_.mock_calls == [call()]
  
subject: add override tests