Fix check_untyped_defs in test_runner

src/_pytest/reports.py

@@ -1,5 +1,6 @@
 from io import StringIO
 from pprint import pprint
+from typing import Any
 from typing import List
 from typing import Optional
 from typing import Tuple
@@ -17,6 +18,7 @@
 from _pytest._code.code import ReprLocals
 from _pytest._code.code import ReprTraceback
 from _pytest._code.code import TerminalRepr
+from _pytest.compat import TYPE_CHECKING
 from _pytest.nodes import Node
 from _pytest.outcomes import skip
 from _pytest.pathlib import Path
@@ -41,9 +43,14 @@ class BaseReport:
     sections = []  # type: List[Tuple[str, str]]
     nodeid = None  # type: str
 
-    def __init__(self, **kw):
+    def __init__(self, **kw: Any) -> None:
         self.__dict__.update(kw)
 
+    if TYPE_CHECKING:
+        # Can have arbitrary fields given to __init__().
+        def __getattr__(self, key: str) -> Any:
+            raise NotImplementedError()
+
     def toterminal(self, out) -> None:
         if hasattr(self, "node"):
             out.line(getslaveinfoline(self.node))  # type: ignore