Android add java library module dependency during test

I try to tun my unit test in android studio 1.2.1.1 using robolectric 3.0-rc2.

My app is split in multiple module.

|---- app (the android app)
|---- common (java library module)

When I run my test I have some references to common module in my activity. But test failed cause of it with a java.lang.NoClassDefFoundError.

So I'm wondering how I should add my module in my dependency.

I tried to add

testCompile(':common')

but nothing changed.