Why is android studio instantiating tests each time?

When I try to run unit tests in android studio, I can see it make, build gradle, etc... all the build stuff, and then I can see an instantiating tests ... which counts up to 9 every time, even if I don't change anything.
In total, running a single test, even without robolectric takes about 30 seconds.
Is there a cache option that I can set on android studio so it doesn't do this?

The reason I'm asking is because sometimes this doesn't happen. Sometimes when I run the tests I just get about 5 seconds of waiting and the tests start with no instantiating or anything, even if I do change stuff, in the tests or otherwise. This works like this then for the full session. After I restart my computer it goes back to normal.