Issue #7449, part 8: don't skip the whole test_asynchat if threading is missing

TestFifo can be executed without the threading module

Lib/test/test_asynchat.py

 # test asynchat
 
-import asyncore, asynchat, socket, threading, time
+import asyncore, asynchat, socket, time
 import unittest
 import sys
 from test import test_support
-
-# Skip tests if thread module does not exist.
-test_support.import_module('thread')
+try:
+    import threading
+except ImportError:
+    threading = None
 
 HOST = test_support.HOST
 SERVER_QUIT = 'QUIT\n'
 
-class echo_server(threading.Thread):
+if threading:
+    class echo_server(threading.Thread):
         # parameter to determine the number of bytes passed back to the
         # client each send
         chunk_size = 1
@@ -57,7 +59,7 @@ class echo_server(threading.Thread):
             conn.close()
             self.sock.close()
 
-class echo_client(asynchat.async_chat):
+    class echo_client(asynchat.async_chat):
 
         def __init__(self, terminator, server_port):
             asynchat.async_chat.__init__(self)
@@ -84,7 +86,7 @@ class echo_client(asynchat.async_chat):
             self.buffer = ""
 
 
-def start_echo_server():
+    def start_echo_server():
         event = threading.Event()
         s = echo_server(event)
         s.start()
@@ -94,6 +96,7 @@ def start_echo_server():
         return s, event
 
 
+@unittest.skipUnless(threading, 'Threading required for this test.')
 class TestAsynchat(unittest.TestCase):
     usepoll = False