mock: Perform patch's autospec checks on __enter__

Currently we're doing the autospec checks on __init__ (if the
target is autospecable), which will require importing modules
in some cases.

The mock.patch's constructor is called when a test module is being
loaded, before any set up could have been run, which can be problematic
in some cases (e.g.: some tested modules are importing platform specific
modules, and they couldn't have been mocked yet).

This patch moves the autospec checks to __enter__, which is executed
after the setUp.

Related-Bug: #1735588

Change-Id: I9e10b34092ad795c7f9e58596fcccf4f37856225

1 files changed, 5 insertions, 5 deletions

diff --git a/oslotest/mock_fixture.py b/oslotest/mock_fixture.py
index ba53dd8..56d6516 100644
--- a/oslotest/mock_fixture.py
+++ b/oslotest/mock_fixture.py
@@ -122,8 +122,10 @@ class _patch(mock.mock._patch):
     https://github.com/testing-cabal/mock/issues/396
     """
 
-    def __init__(self, *args, **kwargs):
-        super(_patch, self).__init__(*args, **kwargs)
+    def __enter__(self):
+        # NOTE(claudiub): we're doing the autospec checks here so unit tests
+        # have a chance to set up mocks in advance (e.g.: mocking platform
+        # specific libraries, which would cause the patch to fail otherwise).
 
         # By default, autospec is None. We will consider it as True.
         autospec = True if self.autospec is None else self.autospec
@@ -146,11 +148,9 @@ class _patch(mock.mock._patch):
 
         # NOTE(claudiub): reset the self.autospec property, so we can handle
         # the autospec scenario ourselves.
-        self._autospec = autospec
         self.autospec = None
 
-    def __enter__(self):
-        if self._autospec:
+        if autospec:
             target = self.getter()
             original_attr = getattr(target, self.attribute)
             eat_self = mock.mock._must_skip(target, self.attribute,