Verification tasks - test Debug/Release unit test

When i run gradle tasks i can see like 50 tasks and in the verification section the last 3 tasks are :

test - Run unit tests for all variants.

testDebugUnitTest - Run unit tests for the debug build.

testReleaseUnitTest - Run unit tests for the release build.

With my project default structure in android studio 2.0.0 i'v few test in each test project, both instrumental and JVM based unit test. I want to understand witch task run witch test and how i configure it?