Allow for nested mocking

The double mocking solution we have now of mocking send and get_adapter
is a bit unusual. One of the problems is that if you have a nested mock
situation then send calling the last send means get_adapter is remocked
again and the outer adapter ends up being the last installed.

To avoid this always go to the real original send function to bypass any
outer installed mockers and make sure our get_adapter function is
triggered.

Change-Id: I47bff5e7da98e5238bd926e22845a7ca34f21940
Closes-Bug: #1642690

requests_mock/mocker.py

@@ -25,6 +25,8 @@
 POST = 'POST'
 PUT = 'PUT'
 
+_original_send = requests.Session.send
+
 
 class MockerCore(object):
     """A wrapper around common mocking functions.
@@ -63,7 +65,7 @@ def __init__(self, **kwargs):
         self._adapter = adapter.Adapter(case_sensitive=case_sensitive)
 
         self._real_http = kwargs.pop('real_http', False)
-        self._real_send = None
+        self._last_send = None
 
         if kwargs:
             raise TypeError('Unexpected Arguments: %s' % ', '.join(kwargs))
@@ -73,10 +75,10 @@ def start(self):
 
         Install the adapter and the wrappers required to intercept requests.
         """
-        if self._real_send:
+        if self._last_send:
             raise RuntimeError('Mocker has already been started')
 
-        self._real_send = requests.Session.send
+        self._last_send = requests.Session.send
 
         def _fake_get_adapter(session, url):
             return self._adapter
@@ -85,8 +87,18 @@ def _fake_send(session, request, **kwargs):
             real_get_adapter = requests.Session.get_adapter
             requests.Session.get_adapter = _fake_get_adapter
 
+            # NOTE(jamielennox): self._last_send vs _original_send. Whilst it
+            # seems like here we would use _last_send there is the possibility
+            # that the user has messed up and is somehow nesting their mockers.
+            # If we call last_send at this point then we end up calling this
+            # function again and the outer level adapter ends up winning.
+            # All we really care about here is that our adapter is in place
+            # before calling send so we always jump directly to the real
+            # function so that our most recently patched send call ends up
+            # putting in the most recent adapter. It feels funny, but it works.
+
             try:
-                return self._real_send(session, request, **kwargs)
+                return _original_send(session, request, **kwargs)
             except exceptions.NoMockAddress:
                 if not self._real_http:
                     raise
@@ -97,7 +109,7 @@ def _fake_send(session, request, **kwargs):
             finally:
                 requests.Session.get_adapter = real_get_adapter
 
-            return self._real_send(session, request, **kwargs)
+            return _original_send(session, request, **kwargs)
 
         requests.Session.send = _fake_send
 
@@ -106,9 +118,9 @@ def stop(self):
 
         This should have no impact if mocking has not been started.
         """
-        if self._real_send:
-            requests.Session.send = self._real_send
-            self._real_send = None
+        if self._last_send:
+            requests.Session.send = self._last_send
+            self._last_send = None
 
     def __getattr__(self, name):
         if name in self._PROXY_FUNCS:

requests_mock/tests/test_mocker.py

@@ -339,3 +339,73 @@ def test_global_case_sensitive(self):
 
             for k, v in query.items():
                 self.assertEqual([v], m.last_request.qs[k])
+
+    def test_nested_mocking(self):
+        url1 = 'http://url1.com/path1'
+        url2 = 'http://url2.com/path2'
+        url3 = 'http://url3.com/path3'
+
+        data1 = 'data1'
+        data2 = 'data2'
+        data3 = 'data3'
+
+        with requests_mock.mock() as m1:
+
+            r1 = m1.get(url1, text=data1)
+
+            resp1a = requests.get(url1)
+            self.assertRaises(exceptions.NoMockAddress, requests.get, url2)
+            self.assertRaises(exceptions.NoMockAddress, requests.get, url3)
+
+            self.assertEqual(data1, resp1a.text)
+
+            # call count = 3 because there are 3 calls above, url 1-3
+            self.assertEqual(3, m1.call_count)
+            self.assertEqual(1, r1.call_count)
+
+            with requests_mock.mock() as m2:
+
+                r2 = m2.get(url2, text=data2)
+
+                self.assertRaises(exceptions.NoMockAddress, requests.get, url1)
+                resp2a = requests.get(url2)
+                self.assertRaises(exceptions.NoMockAddress, requests.get, url3)
+
+                self.assertEqual(data2, resp2a.text)
+
+                with requests_mock.mock() as m3:
+
+                    r3 = m3.get(url3, text=data3)
+
+                    self.assertRaises(exceptions.NoMockAddress,
+                                      requests.get,
+                                      url1)
+                    self.assertRaises(exceptions.NoMockAddress,
+                                      requests.get,
+                                      url2)
+                    resp3 = requests.get(url3)
+
+                    self.assertEqual(data3, resp3.text)
+
+                    self.assertEqual(3, m3.call_count)
+                    self.assertEqual(1, r3.call_count)
+
+                resp2b = requests.get(url2)
+                self.assertRaises(exceptions.NoMockAddress, requests.get, url1)
+                self.assertEqual(data2, resp2b.text)
+                self.assertRaises(exceptions.NoMockAddress, requests.get, url3)
+
+                self.assertEqual(3, m1.call_count)
+                self.assertEqual(1, r1.call_count)
+                self.assertEqual(6, m2.call_count)
+                self.assertEqual(2, r2.call_count)
+                self.assertEqual(3, m3.call_count)
+                self.assertEqual(1, r3.call_count)
+
+            resp1b = requests.get(url1)
+            self.assertEqual(data1, resp1b.text)
+            self.assertRaises(exceptions.NoMockAddress, requests.get, url2)
+            self.assertRaises(exceptions.NoMockAddress, requests.get, url3)
+
+            self.assertEqual(6, m1.call_count)
+            self.assertEqual(2, r1.call_count)