Note why we can't write an automated test for the code path that brings up the…

Note why we can't write an automated test for the code path that brings up the REPL for a bare 'python' call

Lib/test/test_cmd_line_script.py

@@ -143,6 +143,9 @@ class CmdLineTest(unittest.TestCase):
         self.assertIn(expected, out)
 
     def test_stdin_loader(self):
+        # Unfortunately, there's no way to automatically test the fully
+        # interactive REPL, since that code path only gets executed when
+        # stdin in an interactive tty.
         p = spawn_python()
         try:
             p.stdin.write(b"print(__loader__)\n")