Always Check Your Tests Against Faulty Inputs
A while ago, I published a blog post proudly describing the netlab integration test that should check for incorrect OSPF network types in netlab-generated device configurations. Almost immediately, Erik Auerswald pointed out that my test wouldn’t detect that error (it might detect other errors, though) as the OSPF network adjacency is always established even when the adjacent routers have mismatching OSPF network types.
I made one of the oldest testing mistakes: I checked whether my test would work under the correct conditions but not whether it would detect an incorrect condition.
