Expected/Desired Behavior:

When running mn with the --test flag, if a test throws an exception/fails, mn should exit with a nonzero exit code.

Actual Behavior:

If a test throws an exception, the message "Caught exception. Cleaning up..." is printed, but then mn exits with exit code 0.

Detailed Steps to Reproduce the Behavior:

Using the Mininet VM image with version 2.2.2 installed:

1. Create a file example-test.py with the following contents:

   def failing_test(net):
       raise AssertionError('Test failed!')
   
   tests = {'example': failing_test}

2. Run sudo mn --custom example-test.py --test example

   See full output

   *** Creating network
   *** Adding controller
   *** Adding hosts:
   h1 h2
   *** Adding switches:
   s1
   *** Adding links:
   (h1, s1) (h2, s1)
   *** Configuring hosts
   h1 h2
   *** Starting controller
   c0
   *** Starting 1 switches
   s1 ...
   --------------------------------------------------------------------------------
   Caught exception. Cleaning up...
   
   AssertionError: Test failed!
   --------------------------------------------------------------------------------
   *** Removing excess controllers/ofprotocols/ofdatapaths/pings/noxes
   killall controller ofprotocol ofdatapath ping nox_core lt-nox_core ovs-openflowd ovs-controller udpbwtest mnexec ivs 2> /dev/null
   killall -9 controller ofprotocol ofdatapath ping nox_core lt-nox_core ovs-openflowd ovs-controller udpbwtest mnexec ivs 2> /dev/null
   pkill -9 -f "sudo mnexec"
   *** Removing junk from /tmp
   rm -f /tmp/vconn* /tmp/vlogs* /tmp/*.out /tmp/*.log
   *** Removing old X11 tunnels
   *** Removing excess kernel datapaths
   ps ax | egrep -o 'dp[0-9]+' | sed 's/dp/nl:/'
   ***  Removing OVS datapaths
   ovs-vsctl --timeout=1 list-br
   ovs-vsctl --if-exists del-br s1
   ovs-vsctl --timeout=1 list-br
   *** Removing all links of the pattern foo-ethX
   ip link show | egrep -o '([-_.[:alnum:]]+-eth[[:digit:]]+)'
   ( ip link del s1-eth1;ip link del s1-eth2 ) 2> /dev/null
   ip link show
   *** Killing stale mininet node processes
   pkill -9 -f mininet:
   *** Shutting down stale tunnels
   pkill -9 -f Tunnel=Ethernet
   pkill -9 -f .ssh/mn
   rm -f ~/.ssh/mn/*
   *** Cleanup complete.
   
   

3. Run echo $? and notice that the exit code of the previous command was 0 even though an exception was thrown.

Additional Information:

I'm trying to use mn --test to write regression tests for a controller in CI, but this issue makes it difficult to do so because it's hard to automatically tell whether the test succeeded. As a workaround I can search for the string "Caught exception. Cleaning up..." in the output, but this doesn't seem like an ideal solution.