fix: add unittest for it

Signed-off-by: yihong0618 <zouzou0208@gmail.com>

Author: yihong0618

Lib/pdb.py

@@ -2647,12 +2647,12 @@ def set_trace(*, header=None, commands=None):
     just before debugging begins. *commands* is an optional list of
     pdb commands to run when the debugger starts.
     """
-    # Check if we're already in a pdb session by examining the call stack
+    # gh-138641: Check if we're already in a pdb session.
     frame = sys._getframe()
     while frame:
-        if frame.f_code.co_name == 'interaction' and frame.f_code.co_filename.endswith('pdb.py'):
-            # We're already in a pdb session, just print a message and return
-            print("*** Nested breakpoint calls are not supported. "
+        if (frame.f_code.co_name == 'interaction'
+            and frame.f_code.co_filename.endswith('pdb.py')):
+            print("Nested breakpoint calls are not supported. "
                   "Already running in the debugger.", file=sys.stderr)
             return
         frame = frame.f_back
@@ -2672,12 +2672,13 @@ async def set_trace_async(*, header=None, commands=None):
     if they enter the debugger with this function. Otherwise it's the same
     as set_trace().
     """
-    # Check if we're already in a pdb session by examining the call stack
+    # gh-138641: Check if we're already in a pdb session.
     frame = sys._getframe()
     while frame:
-        if frame.f_code.co_name == 'interaction' and frame.f_code.co_filename.endswith('pdb.py'):
+        if (frame.f_code.co_name == 'interaction' and
+            frame.f_code.co_filename.endswith('pdb.py')):
             # We're already in a pdb session, just print a message and return
-            print("*** Nested breakpoint calls are not supported. "
+            print("Nested breakpoint calls are not supported. "
                   "Already running in the debugger.", file=sys.stderr)
             return
         frame = frame.f_back

Lib/test/test_pdb.py

@@ -17,14 +17,14 @@
 import zipfile
 
 from asyncio.events import _set_event_loop_policy
-from contextlib import ExitStack, redirect_stdout
+from contextlib import ExitStack, redirect_stdout, redirect_stderr
 from io import StringIO
 from test import support
 from test.support import has_socket_support, os_helper
 from test.support.import_helper import import_module
 from test.support.pty_helper import run_pty, FakeInput
 from test.support.script_helper import kill_python
-from unittest.mock import patch
+from unittest.mock import Mock, patch
 
 SKIP_CORO_TESTS = False
 
@@ -4539,6 +4539,18 @@ def bar():
             ]))
             self.assertIn('break in bar', stdout)
 
+    def test_nested_breakpoint_calls(self):
+        # gh-138641 pdb.set_trace() called when already in the debugger
+        mock_frame = Mock()
+        mock_frame.f_code.co_name = 'interaction'
+        mock_frame.f_code.co_filename = '/path/to/pdb.py'
+        mock_frame.f_back = None
+        captured_stderr = io.StringIO()
+        with redirect_stderr(captured_stderr):
+            with patch('sys._getframe', return_value=mock_frame):
+                pdb.set_trace()
+        stderr_content = captured_stderr.getvalue()
+        self.assertIn("Nested breakpoint calls are not supported", stderr_content)
 
 class ChecklineTests(unittest.TestCase):
     def setUp(self):