List mockedList = mock(List.class);

Mockito.when(mockedList.get(0))
        .thenReturn("one")
        .thenReturn("two")
        .thenThrow(new RuntimeException());

System.out.println(mockedList.get(0)); // one
System.out.println(mockedList.get(0)); // two
System.out.println(mockedList.get(0)); // RuntimeExceptionが発生する