Question: I'm trying to understand the difference between these two mock constructs and when is it appropriate to use either. I tested it in the interpreter, e.g.: >>> mm = mock.MagicMock(spec=list) >>> ca = mock.create_autospec(list) >>> mm <MagicMock spec='list' id='140372375801232'> >>> mm() <MagicMock name='mock()' id='140372384057808'> >>> mm.append() <MagicMock name='mock.append()' id='140372375724720'> >>> mm().append() <MagicMock name='mock().append()' id='140372375753104'> >>> ca <MagicMock spec='list' id='140372384059248'> >>> ca() <NonCallableMagicMock name='mock()' spec='list' id='140372384057040'> >>> ca.append() <MagicMock name='mock.append()' id='140372375719744'> >>> ca().append() <MagicMock name='mock().append()' id='140372375796848'> >>>  But I can't understand why "constructing" the mock created using create_autospec gives me a NonCallableMagicMock and the MagicMock gives me more MagicMock. The documentation isn't helping much.

Answer: The main difference between using the spec argument and using create_autospec is recursiveness. In the first case, the object itself is specced, while the called object is not: >>> mm = mock.MagicMock(spec=list) >>> mm <MagicMock spec='list' id='2868486557120'> >>> mm.foo Traceback (most recent call last): File "<stdin>", line 1, in <module> File "c:\Python\Python38\lib\unittest\mock.py", line 635, in __getattr__ raise AttributeError("Mock object has no attribute %r" % name) AttributeError: Mock object has no attribute 'foo' >>> mm.append <MagicMock name='mock.append' id='2868486430240'> >>> mm.append.foo <MagicMock name='mock.append.foo' id='2868486451408'>  In the second case, the called objects are also specced (lazily): >>> ca = mock.create_autospec(list) >>> ca <MagicMock spec='list' id='2868486254848'> >>> ca.foo Traceback (most recent call last): File "<stdin>", line 1, in <module> File "c:\Python\Python38\lib\unittest\mock.py", line 635, in __getattr__ raise AttributeError("Mock object has no attribute %r" % name) AttributeError: Mock object has no attribute 'foo' >>> ca.append <MagicMock name='mock.append' spec='method_descriptor' id='2868486256336'> >>> ca.append.foo Traceback (most recent call last): File "<stdin>", line 1, in <module> File "c:\Python\Python38\lib\unittest\mock.py", line 635, in __getattr__ raise AttributeError("Mock object has no attribute %r" % name) AttributeError: Mock object has no attribute 'foo'  There is one caveat, that is shown in your example code. If you use create_autospec as shown here, it behaves as if the object is a class, not an instance, so you are able to call it (creating an instance): >>> ca = mock.create_autospec(list) >>> ca() <NonCallableMagicMock name='mock()' spec='list' id='2868485877280'>  If you want to behave it like an instance, you have to use instance=True: >>> ca = mock.create_autospec(list, instance=True) >>> ca <NonCallableMagicMock spec='list' id='2868485875024'> >>> ca() Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: 'NonCallableMagicMock' object is not callable  Note that using mock.patch with autospec=True creates a mock that behaves like the one created using mock.create_autospec, as described in the documentation. Also note that the return value of a call is always a MagicMock, regardless of the return value of the real call. So, even if a function returns None, like list.append, a mock is returned if calling the method from a mock, regardless of the spec.