patch 7.4.1398
Problem:    The close-cb option is not implemented yet.
Solution:   Implemente close-cb. (Yasuhiro Matsumoto)
diff --git a/src/testdir/test_channel.py b/src/testdir/test_channel.py
index 26c7dea..9a3c921 100644
--- a/src/testdir/test_channel.py
+++ b/src/testdir/test_channel.py
@@ -140,6 +140,10 @@
                         print("sending: {}".format(cmd))
                         self.request.sendall(cmd.encode('utf-8'))
                         response = ""
+                    elif decoded[1] == 'close me':
+                        print("closing")
+                        self.request.close()
+                        response = ""
                     elif decoded[1] == 'wait a bit':
                         time.sleep(0.2)
                         response = "waited"