pythongh-102864: Add switching frame test for pdb (python#119564)

Lib/test/test_pdb.py

@@ -2555,7 +2555,7 @@ def test_pdb_issue_gh_94215():
 def test_pdb_issue_gh_101673():
     """See GH-101673
 
-    Make sure ll won't revert local variable assignment
+    Make sure ll and switching frames won't revert local variable assignment
 
     >>> def test_function():
     ...    a = 1
@@ -2565,6 +2565,10 @@ def test_pdb_issue_gh_101673():
     ...     '!a = 2',
     ...     'll',
     ...     'p a',
+    ...     'u',
+    ...     'p a',
+    ...     'd',
+    ...     'p a',
     ...     'continue'
     ... ]):
     ...     test_function()
@@ -2577,6 +2581,16 @@ def test_pdb_issue_gh_101673():
       3  ->        import pdb; pdb.Pdb(nosigint=True, readrc=False).set_trace()
     (Pdb) p a
     2
+    (Pdb) u
+    > <doctest test.test_pdb.test_pdb_issue_gh_101673[1]>(11)<module>()
+    -> test_function()
+    (Pdb) p a
+    *** NameError: name 'a' is not defined
+    (Pdb) d
+    > <doctest test.test_pdb.test_pdb_issue_gh_101673[0]>(3)test_function()
+    -> import pdb; pdb.Pdb(nosigint=True, readrc=False).set_trace()
+    (Pdb) p a
+    2
     (Pdb) continue
     """