Added a test of maps between databases.
Added a test of maps between databases.

RitwikGupta/pygr,cjlee112/pygr,theoryno3/pygr,GenDataPro/pygr,GenDataPro/pygr,theoryno3/pygr,RitwikGupta/pygr,cjlee112/pygr,cjlee112/pygr,GenDataPro/pygr,theoryno3/pygr,RitwikGupta/pygr,cjlee112/pygr