How to mock method in extended trait with Mockito

How can I mock dependend traits with mockito? I have two traits:

 trait A {
    def a = 1
  }

  trait B extends A {
    def b = {
      // do things
      a
      // do things
    }
  }

Now, I want to test Trait B. And I want to verify, that A.a() gets called:

class SmallTest extends FunSuite with MockitoSugar {
  test("prove, that a gets called") {
    val mockA = mock[A]
    val b = new B with mockA {}  // This won't compile
    b.b
    verify(mockA).a
  }
}

This example won't compile. But how would I "inject" my mock otherwise?