add test

Author: ashm-dev

Lib/test/test_struct.py

@@ -800,6 +800,24 @@ def test_c_complex_round_trip(self):
                     round_trip = struct.unpack(f, struct.pack(f, z))[0]
                     self.assertComplexesAreIdentical(z, round_trip)
 
+    def test_endian_table_init_subinterpreters(self):
+        # Verify that struct works correctly in subinterpreters after
+        # once-only endian table initialization (gh-140260).
+        # Use struct in the main interpreter first.
+        self.assertEqual(struct.unpack('>i', struct.pack('>i', 1))[0], 1)
+        self.assertEqual(struct.unpack('<i', struct.pack('<i', 1))[0], 1)
+
+        code = (
+            "import struct\n"
+            "x = struct.pack('>i', 1)\n"
+            "assert struct.unpack('>i', x)[0] == 1\n"
+            "y = struct.pack('<i', 1)\n"
+            "assert struct.unpack('<i', y)[0] == 1\n"
+        )
+        for _ in range(3):
+            ret = support.run_in_subinterp(code)
+            self.assertEqual(ret, 0)
+
 
 class UnpackIteratorTest(unittest.TestCase):
     """