From fe830674abd4926d96d38f9992f3e31b00cd891a Mon Sep 17 00:00:00 2001
From: Stephen Finucane <stephenfin@redhat.com>
Date: Thu, 25 Feb 2021 11:37:42 +0000
Subject: [PATCH] Fix tests on Python 3.9

I'm not entirely sure this is correct, but it's the only thing I can
find related to changes in classmethod in Python 3.9.

Signed-off-by: Stephen Finucane <stephenfin@redhat.com>
---
 fixtures/_fixtures/monkeypatch.py            |  9 +++-
 fixtures/tests/_fixtures/test_monkeypatch.py | 48 ++++++++++++++------
 2 files changed, 42 insertions(+), 15 deletions(-)

diff --git a/fixtures/_fixtures/monkeypatch.py b/fixtures/_fixtures/monkeypatch.py
index b5e8564..710a79c 100644
--- a/fixtures/_fixtures/monkeypatch.py
+++ b/fixtures/_fixtures/monkeypatch.py
@@ -83,9 +83,11 @@ def _coerce_values(obj, name, new_value, sentinel):
             # bound state rather than having it bound to the new object
             # it has been patched onto.
             captured_method = new_value
+
             @functools.wraps(old_value)
             def avoid_get(*args, **kwargs):
                 return captured_method(*args, **kwargs)
+
             new_value = avoid_get
 
     return (new_value, old_value)
@@ -138,18 +140,21 @@ def _setUp(self):
             __import__(location, {}, {})
         except ImportError:
             pass
+
         components = location.split('.')
         current = __import__(components[0], {}, {})
         for component in components[1:]:
             current = getattr(current, component)
         sentinel = object()
-        new_value, old_value = _coerce_values(current, attribute,
-                self.new_value, sentinel)
+        new_value, old_value = _coerce_values(
+            current, attribute, self.new_value, sentinel)
+
         if self.new_value is self.delete:
             if old_value is not sentinel:
                 delattr(current, attribute)
         else:
             setattr(current, attribute, new_value)
+
         if old_value is sentinel:
             self.addCleanup(self._safe_delete, current, attribute)
         else:
diff --git a/fixtures/tests/_fixtures/test_monkeypatch.py b/fixtures/tests/_fixtures/test_monkeypatch.py
index 6f11fab..746f6dd 100644
--- a/fixtures/tests/_fixtures/test_monkeypatch.py
+++ b/fixtures/tests/_fixtures/test_monkeypatch.py
@@ -14,6 +14,7 @@
 # limitations under that license.
 
 import functools
+import sys
 
 import testtools
 from testtools.matchers import Is
@@ -32,7 +33,7 @@ def foo_cls(cls): pass
 
 class D(object):
     def bar(self): pass
-    def bar_two_args(self, arg):
+    def bar_two_args(self, arg=None):
         return (self, arg)
     @classmethod
     def bar_cls(cls):
@@ -188,14 +189,27 @@ def test_patch_classmethod_with_classmethod(self):
             'fixtures.tests._fixtures.test_monkeypatch.C.foo_cls',
             D.bar_cls_args)
         with fixture:
-            cls, target_class = C.foo_cls()
-            self.expectThat(cls, Is(D))
-            self.expectThat(target_class, Is(C))
-            cls, target_class = C().foo_cls()
-            self.expectThat(cls, Is(D))
-            self.expectThat(target_class, Is(C))
-        self._check_restored_static_or_class_method(oldmethod, oldmethod_inst,
-                C, 'foo_cls')
+            # Python 3.9 changes the behavior of the classmethod decorator so
+            # that it now honours the descriptor binding protocol [1].
+            # This means we're now going to call the monkeypatched classmethod
+            # the way we would have if it hadn't been monkeypatched: simply
+            # with the class
+            #
+            # https://bugs.python.org/issue19072
+            if sys.version_info >= (3, 9):
+                cls, = C.foo_cls()
+                self.expectThat(cls, Is(D))
+                cls, = C().foo_cls()
+                self.expectThat(cls, Is(D))
+            else:
+                cls, target_class = C.foo_cls()
+                self.expectThat(cls, Is(D))
+                self.expectThat(target_class, Is(C))
+                cls, target_class = C().foo_cls()
+                self.expectThat(cls, Is(D))
+                self.expectThat(target_class, Is(C))
+        self._check_restored_static_or_class_method(
+            oldmethod, oldmethod_inst, C, 'foo_cls')
 
     def test_patch_classmethod_with_function(self):
         oldmethod = C.foo_cls
@@ -222,12 +236,20 @@ def test_patch_classmethod_with_boundmethod(self):
         with fixture:
             slf, cls = C.foo_cls()
             self.expectThat(slf, Is(d))
-            self.expectThat(cls, Is(C))
+            # See note in test_patch_classmethod_with_classmethod on changes in
+            # Python 3.9
+            if sys.version_info >= (3, 9):
+                self.expectThat(cls, Is(None))
+            else:
+                self.expectThat(cls, Is(C))
             slf, cls = C().foo_cls()
             self.expectThat(slf, Is(d))
-            self.expectThat(cls, Is(C))
-        self._check_restored_static_or_class_method(oldmethod, oldmethod_inst,
-                C, 'foo_cls')
+            if sys.version_info >= (3, 9):
+                self.expectThat(cls, Is(None))
+            else:
+                self.expectThat(cls, Is(C))
+        self._check_restored_static_or_class_method(
+            oldmethod, oldmethod_inst, C, 'foo_cls')
 
     def test_patch_function_with_staticmethod(self):
         oldmethod = fake_no_args