Add mockery library for testing.
Add mockery library for testing.

Added mockery to composer.json.

sonuku/stapler,simudream/stapler,AndreasHeiberg/stapler,oschettler/stapler,aozisik/stapler,flaxandteal/stapler,neerajgoyal12/stapler,CodeSleeve/stapler,riyan8250/stapler,InMoji/stapler