A modern programming language that makes developers happier.

kotlinlang

Gradle's an developer automation tool.
I don't want to have to remember a bunch of flags to enable/disable certain tests based upon what's up to date or not.
The build tool can, given its knowledge of the dependencies between projects, intrlegently determine when certain tests are up to date or not.

I guess you could say that Gradle assumes that your are unit testing in your tests so the assumed inputs to the tests can be represented as inputs.