Sadly there is no such command. Django has no way of telling which apps are "yours" versus which are someone else's.
What I would suggest is writing a new management command, call it mytest. Then create a new setting MY_INSTALLED_APPS. The mytest command will just run the test for every app in MY_INSTALLED_APPS. You'll want the mytest command to subclass django.core.management.base.AppCommand. django.core.management.call_command will also be helpful.
The only problem with this method is that you will have to constantly maintain the MY_INSTALLED_APPS setting to make sure it is correct.