$expand Query for entityset

Hi experts,

short question - is it possible to use the exand query also for entityset?

For example:

/sap/opu/odata/sap/ZWWW_TEST/test/$expand=test2

--> I want to expand test for all entries, not a specific one.

At the moment, I get error "test is not a entity, it's an entityset"

Maybe something's missing :-)

Thanks

Michael