如何使用MockitoJUnitRunner模拟unmodifiableMap

Question

Class Test {

 private A a;

 private B b; 

}

Class B{

 private final Map<String, Integer> sampleMap = new HashMap();

 public Map<String, Integer> getSampleMap() {

      return Collections.unmodifiableMap(this.sampleMap);
  }

}

如何通过模拟unModifiable getSampleMap模拟测试对象。我需要创建和设置键/值对。