Mockito calling real method instead of mock

I'm trying to mock one of my classes in the following manner.

class A {
....
...
 public Fruits getFruitsByID(String fruitId)
    //get fruit type from DB
}

Now class B tries to access this method in class A in the following manner

    class B{

    A fruitConn;
    B(A fruitConnLocal)
    { 
       fruitConn=fruitConnLocal;
    }
    Response getFruits ( String fruitID) {
       Fruits fruit= fruitConn.getFruitsByID(fruitID);
..../// send response with fruits.
    }

Here's how I try to mock it using Mockito.

 classBTest {
  public void testGetFruits(){
   A fruitConn= mock(fruitConn.class);
   Fruit fruit= mock(Fruit.class);
   B testB= new B(fruitConn);
   when(fruitConn.getFruitsByID(Matchers.anyString()).thenReturn(fruit);
 // here the actual method getFruitsByID is 
//called instead of the mock.. why?
   AssertNotEmpty(B.getFruits("test"));
}
}

P.S. Im very new to mockito so any help would be greatly appreciated.