Adding a note to `testing.md` regarding failing handlers

docs/testing.md

@@ -10,3 +10,11 @@ To log in, use `admin` as both the username & password.
 
 
 As support for other operating systems/distributions is written, they will be added as options for testing.
+
+## Caveats
+It is expected that the following two handlers, triggered at the end of the test run will fail: 
+- `restart sensu-server service`
+- `restart sensu-api service`
+
+Both these handlers use the `delegate_to` directive, which does not play nice with Vagrant.  
+This __is__ expected to work in real deployments.