unittest: restore UnitTestFunction.obj to return unbound rather than bound method

changelog/9610.bugfix.rst

@@ -0,0 +1,3 @@
+Restore `UnitTestFunction.obj` to return unbound rather than bound method.
+Fixes a crash during a failed teardown in unittest TestCases with non-default `__init__`.
+Regressed in pytest 7.0.0.

src/_pytest/unittest.py

@@ -185,6 +185,15 @@ class TestCaseFunction(Function):
     _excinfo: Optional[List[_pytest._code.ExceptionInfo[BaseException]]] = None
     _testcase: Optional["unittest.TestCase"] = None
 
+    def _getobj(self):
+        assert self.parent is not None
+        # Unlike a regular Function in a Class, where `item.obj` returns
+        # a *bound* method (attached to an instance), TestCaseFunction's
+        # `obj` returns an *unbound* method (not attached to an instance).
+        # This inconsistency is probably not desirable, but needs some
+        # consideration before changing.
+        return getattr(self.parent.obj, self.originalname)  # type: ignore[attr-defined]
+
     def setup(self) -> None:
         # A bound method to be called during teardown() if set (see 'runtest()').
         self._explicit_tearDown: Optional[Callable[[], None]] = None

testing/test_unittest.py

@@ -1472,3 +1472,29 @@ def test_cleanup_called_the_right_number_of_times():
     passed, skipped, failed = reprec.countoutcomes()
     assert failed == 2
     assert passed == 1
+
+
+def test_traceback_pruning(pytester: Pytester) -> None:
+    """Regression test for #9610 - doesn't crash during traceback pruning."""
+    pytester.makepyfile(
+        """
+        import unittest
+
+        class MyTestCase(unittest.TestCase):
+            def __init__(self, test_method):
+                unittest.TestCase.__init__(self, test_method)
+
+        class TestIt(MyTestCase):
+            @classmethod
+            def tearDownClass(cls) -> None:
+                assert False
+
+            def test_it(self):
+                pass
+        """
+    )
+    reprec = pytester.inline_run()
+    passed, skipped, failed = reprec.countoutcomes()
+    assert passed == 1
+    assert failed == 1
+    assert reprec.ret == 1