Currently it is not possible to overwrite the resource mapping being configured in AemContextImpl.setUp().
For some test cases it would be useful have some mapping there.
The problem is, that the configuration of the ResourceResolverFactoryActivator must happen before SlingContextImpl.setUp() is being called. If the configuration takes place afterwards, that will have no effect on the already created resource resolver factory.
This affects aem-mock-1.7.0.