add test__dns.py

greentest/test__dns.py

+import greentest
+import socket as real_socket
+from gevent import socket
+
+class TestHostname(greentest.TestCase):
+    switch_expected = False
+
+    def test_gethostbyname_hostname(self):
+        hostname = real_socket.gethostname()
+        real_ip = real_socket.gethostbyname(hostname)
+        ip = socket.gethostbyname(hostname)
+        assert real_ip == ip, (real_ip, ip)
+
+if __name__=='__main__':
+    greentest.main()