List mockedList = mock(List.class);

// 基本形
Mockito.when(mockedList.get(0))
        .thenReturn("one")
        .thenReturn("two")
        .thenReturn("three");

// 短縮形
Mockito.when(mockedList.get(0)).thenReturn("one", "two", "three");

System.out.println(mockedList.get(0)); // one
System.out.println(mockedList.get(0)); // two
System.out.println(mockedList.get(0)); // three
System.out.println(mockedList.get(0)); // three