Using Python mock to spy on calls to an existing object

Question

I'm using the Python mock module for tests. I would like to replace an active object with a mock, and automatically have all calls made to the mock object forwarded to the original object. I think this is called a "Spy" in standard testing terminology. At the moment I'm doing inside a test:

# Insert a mock replacement orig_active_attr = server.active_attr server.active_attr = mock.Mock()  # Set up side effects to 'proxy' to the original object server.active_attr.meth1.side_effect = orig_active_attr.meth1 server.active_attr.meth2.side_effect = orig_active_attr.meth2  # Call the method being tested server.method_being_tested()  # Assert stuff on the mock. server.active_attr.meth2.assert_called_once() 

It would be nice if all method calls on the mock could be forwarded to the live object automatically without the boilerplate.

Answer 1

I seem to have stumbled across the solution:

import mock  class A(object):     def meth(self, a):         return a a = A() ma = mock.Mock(wraps=a) 

Seems to work okay for functions, methods and properties, but not for class or instance attributes.

See the documentation.

Answer 2

You can use patch.object(wraps=obj_instance) as suggested in Spying on instance methods with Python's mock module.

For example:

from mock import patch  class Foo(object):     def bar(self, x, y):         return x + y + 1  def test_bar():     foo = Foo()     with patch.object(foo, 'bar', wraps=foo.bar) as wrapped_foo:         foo.bar(1, 2)         wrapped_foo.assert_called_with(1, 2)