Method object disappears when it's mocked out by unittest.mock and patched by ddtrace

Summary of problem

I encountered this issue when trying to instrument a pytest test suite for CI visibility. There's a test case that mocks out the POST handler of a Django view class to confirm that it was called, and it started failing when I invoked the test suite with --ddtrace --ddtrace-patch-all. Specifying --ddtrace alone did not result in a test failure. As you can see below, I was able to narrow it down to a reproducible example that doesn't involve pytest or Django.

I can likely fix the test by not relying on mocking (which is better anyways in this case), but wanted to report the issue in case this is something unexpected and should be fixed on dd-trace-py's end.

Which version of dd-trace-py are you using?

1.7.2 (the version used by the repl.it project below)

Which version of pip are you using?

21.2.dev0 (the version used by the repl.it project below)

Which libraries and their versions are you using?

`poetry run pip freeze` (what the repl.it project below outputs)

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@ https://files.pythonhosted.org/packages/c8/27/be6ddbcf60115305205de79c29004a0c6bc53cec814f733467b1bb89386d/Werkzeug-2.2.2-py3-none-any.whl#sha256=f979ab81f58d7318e064e99c4506445d60135ac5cd2e177a2de0089bfd4c9bd5 whatthepatch @ https://files.pythonhosted.org/packages/93/f7/3276ba8d661f459afb171af169a7f68a390ede84c5510baf4575ce3316df/whatthepatch-1.0.3-py3-none-any.whl#sha256=465e075f612bc145905cf2574ea1c5a0122b9eb41959408d676b3b929eae0d8e xmltodict @ https://files.pythonhosted.org/packages/94/db/fd0326e331726f07ff7f40675cd86aa804bfd2e5016c727fa761c934990e/xmltodict-0.13.0-py2.py3-none-any.whl#sha256=aa89e8fd76320154a40d19a0df04a4695fb9dc5ba977cbb68ab3e4eb225e7852 yapf @ https://files.pythonhosted.org/packages/47/88/843c2e68f18a5879b4fbf37cb99fbabe1ffc4343b2e63191c8462235c008/yapf-0.32.0-py2.py3-none-any.whl#sha256=8fea849025584e486fd06d6ba2bed717f396080fd3cc236ba10cb97c4c51cf32 yarl @ https://files.pythonhosted.org/packages/b5/e0/6ea3832faed10de6a06cd407c660e6978d5538fe7489e934fb9967c8bb8b/yarl-1.8.2-cp310-cp310-manylinux_2_17_x86_64.manylinux2014_x86_64.whl#sha256=6c4fcfa71e2c6a3cb568cf81aadc12768b9995323186a10827beccf5fa23d4f8 ```

How can we reproduce your problem?

MCVE: https://replit.com/@ento/FlawedHarmfulOperation

This has three examples:

Invoking a mocked out Django view without tracing: succeeds
Invoking a mocked out Django view with tracing: fails
Invoking a simple method after mocking it out and setting up tracing: fails

The third example is what's essentially happening with the second example: when Django's default request dispatcher tries to get the correct handler method for the current request's HTTP verb, it can't find MockedView.get and instead returns http_method_not_allowed.

main.py

```py import os from unittest import mock os.environ["AWS_LAMBDA_FUNCTION_NAME"] = "forcing_ddtrace_to_use_log_writer" import django from ddtrace import Pin, tracer from ddtrace.contrib import trace_utils from ddtrace.contrib.django.patch import traced_as_view, traced_func from django.conf import settings from django.http import HttpResponse from django.test import RequestFactory from django.views import View rf = RequestFactory() try: settings.configure() except RuntimeError: pass class MockedView(View): def get(self, request): return HttpResponse("hello") def request_get(): with mock.patch.object(MockedView, "get") as mock_get: view = MockedView.as_view() request = rf.get("/") response = view(request) try: assert mock_get.called, "MockedView.get() should've been called" print("o", "got", response) except AssertionError: print("! mocked 'get' method was not called") print("###", "before patching", "###") request_get() print("") Pin().onto(django) trace_utils.wrap(django, "views.generic.base.View.as_view", traced_as_view(django)) print("###", "after patching", "###") request_get() print("") print("###", "raw object", "###") class A: def foo(): print("hello foo") print("before patching: getattr(A(), 'foo', None) =", getattr(A(), "foo", None)) with mock.patch.object(A, "foo") as mock_foo: print("after patching: getattr(A(), 'foo', None) =", getattr(A(), "foo", None)) trace_utils.wrap(A, "foo", traced_func(django, name="foo", resource="A")) print("after wrapping: getattr(A(), 'foo', None) =", getattr(A(), "foo", None)) A().foo() print("mock_foo.called", mock_foo.called) ```

What is the result that you get?

### before patching ###
o got <MagicMock name='get()' id='140623340048208'>

### after patching ###
Method Not Allowed (GET): /
{"traces": [ ELIDED FOR BREVITY ]}
! mocked 'get' method was not called

### raw object ###
before patching: getattr(A(), 'foo', None) = <bound method A.foo of <__main__.A object at 0x7fe56bec8b10>>
after patching: getattr(A(), 'foo', None) = <MagicMock name='foo' id='140623334876944'>
after wrapping: getattr(A(), 'foo', None) = None
Traceback (most recent call last):
  File "mocked_view.py", line 67, in <module>
    A().foo()
AttributeError: 'MagicMock' object has no attribute '__get__'

What is the result that you expected?

### before patching ###
o got <MagicMock name='get()' id='139930083200720'>

### after patching ###
{"traces": [ ELIDED FOR BREVITY ]}
o got <MagicMock name='get()' id='139930078059280'>

### raw object ###
before patching: getattr(A(), 'foo', None) = <bound method A.foo of <__main__.A object at 0x7f44029899d0>>
after patching: getattr(A(), 'foo', None) = <MagicMock name='foo' id='139930078097488'>
after wrapping: getattr(A(), 'foo', None) = <MagicMock name='foo' id='139930078097488'>
mock_foo.called True

DataDog / dd-trace-py