Add undocumented methods and make types more specific in 2/unittest (#3550)

stdlib/3/unittest/result.pyi

@@ -1,11 +1,12 @@
-from typing import List, Optional, Tuple, Type
+from typing import List, Optional, Tuple, Type, Union
 from types import TracebackType
 import unittest.case
 
 
-_SysExcInfoType = Tuple[Optional[Type[BaseException]],
-                        Optional[BaseException],
-                        Optional[TracebackType]]
+_SysExcInfoType = Union[
+    Tuple[Type[BaseException], BaseException, TracebackType],
+    Tuple[None, None, None],
+]
 
 
 class TestResult: