我有办法 getAggregateValue 这需要一个复合的分类（ElasticSearch）和一个键。
编写单元测试；我想嘲笑 var aggregation = aggregations.get(aggKey); 所以它返回一个 ParsedSum 为给定的“aggkey”键入。我该怎么做？

private Summary mapCompositeAggregationToFieldSummary(CompositeAggregation.Bucket bucket) {

        var field1 = getAggregateValue(bucket.getAggregations(), "field1");
   }

    private Long getAggregateValue(Aggregations aggregations, String aggKey) {
        var aggregation = aggregations.get(aggKey);
        if (aggregation == null) {
            return 0L;
        }
        return (long)(((ParsedSum)(aggregation)).getValue());
    }