Add test for __cache__ to model tests.
Add test for __cache__ to model tests.

TouK/vumi,harrissoerja/vumi,vishwaprakashmishra/xmatrix,harrissoerja/vumi,vishwaprakashmishra/xmatrix,TouK/vumi,vishwaprakashmishra/xmatrix,harrissoerja/vumi,TouK/vumi