public void test_addProcessingTime_multiple() {
        DocList docList = new DocList();

        docList.addProcessingTime(10);
        assertEquals(10, docList.getProcessingTime());

        docList.addProcessingTime(20);
        assertEquals(30, docList.getProcessingTime());

        docList.addProcessingTime(5);
        assertEquals(35, docList.getProcessingTime());
    }

    public void test_addContentSize_negative() {

    }

    /**
     * Adds to the total processing time of this document list.
     *
     * @param processingTime the processing time to add in milliseconds
     */
    public void addProcessingTime(final long processingTime) {
        this.processingTime += processingTime;
    }

    /**
     * Returns a string representation of this DocList including metrics and content.
     *