cleaned up and commented test_nat.py; added check for connectivity before running test

examples/test/test_nat.py

@@ -1,44 +1,32 @@
 #!/usr/bin/env python
 
-"""TEST"""
+"""
+Test for nat.py
+"""
 
 import unittest
 import pexpect
-#from time import sleep
+from mininet.util import quietRun
-from mininet.log import setLogLevel
-#from mininet.net import Mininet
-#from mininet.node import CPULimitedHost
-#from mininet.link import TCLink
 
-#from mininet.examples.simpleperf import SingleSwitchTopo
+destIP = '8.8.8.8' # Google DNS
 
 class testNAT( unittest.TestCase ):
-    "Test ping with single switch topology (common code)."
 
     prompt = 'mininet>'
 
-    # skip if 8.8.8.8 unreachable
+    @unittest.skipIf( '0 received' in quietRun( 'ping -c 1 %s' % destIP ), 
+                      'Destination IP is not reachable' )
     def testNAT( self ):
+        "Attempt to ping an IP on the Internet and verify 0% packet loss"
         p = pexpect.spawn( 'python -m mininet.examples.nat' )
         p.expect( self.prompt )
-        p.sendline( 'h1 ping -c 1 8.8.8.8' )
+        p.sendline( 'h1 ping -c 1 %s' % destIP )
         p.expect ( '(\d+)% packet loss' )
         percent = int( p.match.group( 1 ) ) if p.match else -1
         p.expect( self.prompt )
         p.sendline( 'exit' )
         p.wait()
         self.assertEqual( percent, 0 )
-    '''
-    def testTopo( self ):
-        topo = SingleSwitchTopo(n=4)
-        net = Mininet(topo=topo,
-                  host=CPULimitedHost, link=TCLink)
-        net.start()
-        h1, h4 = net.get('h1', 'h4')
-        h1.cmd( 'ping -c 1 %s' % h4.IP() )
-        net.stop()
-    '''
 
 if __name__ == '__main__':
-    setLogLevel( 'warning' )
     unittest.main()