fix: add a test case

Signed-off-by: Frost Ming <[email protected]>

Author: frostming

Lib/test/test_remote_pdb.py

@@ -1590,5 +1590,17 @@ def test_attach_to_process_with_colors(self):
         self.assertNotIn("while x == 1", output["client"]["stdout"])
         self.assertIn("while x == 1", re.sub("\x1b[^m]*m", "", output["client"]["stdout"]))
 
+    def test_attach_to_non_existent_process(self):
+        with force_color(False):
+            result = subprocess.run([sys.executable, "-m", "pdb", "-p", "999999"], text=True, capture_output=True)
+        self.assertNotEqual(result.returncode, 0)
+        error = (
+            "The specified process cannot be attached to due to insufficient permissions."
+            if sys.platform == "darwin" else
+            "Cannot attach to pid 999999, please make sure that the process exists"
+        )
+        self.assertIn(error, result.stdout)
+
+
 if __name__ == "__main__":
     unittest.main()