[3.6] bpo-30065: Fixed arguments validation in _posixsubprocess.fork_exec(). (GH-1110) (#1186)

(cherry picked from commit 66bffd1)
diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py
index 3c871dd..d8d6d82 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -2431,7 +2431,7 @@
                 with self.assertRaises(TypeError):
                     _posixsubprocess.fork_exec(
                         args, exe_list,
-                        True, [], cwd, env_list,
+                        True, (), cwd, env_list,
                         -1, -1, -1, -1,
                         1, 2, 3, 4,
                         True, True, func)
@@ -2443,6 +2443,16 @@
     def test_fork_exec_sorted_fd_sanity_check(self):
         # Issue #23564: sanity check the fork_exec() fds_to_keep sanity check.
         import _posixsubprocess
+        class BadInt:
+            first = True
+            def __init__(self, value):
+                self.value = value
+            def __int__(self):
+                if self.first:
+                    self.first = False
+                    return self.value
+                raise ValueError
+
         gc_enabled = gc.isenabled()
         try:
             gc.enable()
@@ -2453,6 +2463,7 @@
                 (18, 23, 42, 2**63),  # Out of range.
                 (5, 4),  # Not sorted.
                 (6, 7, 7, 8),  # Duplicate.
+                (BadInt(1), BadInt(2)),
             ):
                 with self.assertRaises(
                         ValueError,