Add a typing-compatible mechanism for ad-hoc attributes on various objects

pytest has several instances where plugins set their own attributes on
objects they receive in hooks, like nodes and config. Since plugins are
detached from these object's definition by design, this causes a problem
for type checking because these attributes are not defined and mypy
complains.

Fix this by giving these objects a "store" which can be used by plugins
in a type-safe manner.

Currently this mechanism is private. We can consider exposing it at a
later point.

1 files changed, 4 insertions, 2 deletions

diff --git a/src/_pytest/unittest.py b/src/_pytest/unittest.py
index a5512e944..2047876e5 100644
--- a/src/_pytest/unittest.py
+++ b/src/_pytest/unittest.py
@@ -14,6 +14,8 @@ from _pytest.outcomes import xfail
 from _pytest.python import Class
 from _pytest.python import Function
 from _pytest.runner import CallInfo
+from _pytest.skipping import skipped_by_mark_key
+from _pytest.skipping import unexpectedsuccess_key
 
 
 def pytest_pycollect_makeitem(collector, name, obj):
@@ -174,7 +176,7 @@ class TestCaseFunction(Function):
         try:
             skip(reason)
         except skip.Exception:
-            self._skipped_by_mark = True
+            self._store[skipped_by_mark_key] = True
             self._addexcinfo(sys.exc_info())
 
     def addExpectedFailure(self, testcase, rawexcinfo, reason=""):
@@ -184,7 +186,7 @@ class TestCaseFunction(Function):
             self._addexcinfo(sys.exc_info())
 
     def addUnexpectedSuccess(self, testcase, reason=""):
-        self._unexpectedsuccess = reason
+        self._store[unexpectedsuccess_key] = reason
 
     def addSuccess(self, testcase):
         pass