Maybe is too soon to ask, but as Jack and Jill was announced today I get very excited with it. I really want to go for it, but they also state:
Various tools that read .class files (such as JaCoCo, Mockito, and some lint checks) are currently not compatible with the Jack compiler.
There is already an mockito alternative for jack compiler ?
Mockito doesn't generate any byte code at compile time and hence is not affected by the used compiler. Same holds true for dexmaker. (they don't have any hooks into Gradle during build)
So you can simply continue to use Mockito, even with Jack compiler. Note that I have a test project which confirms this.