public List<Float> getSingleReportData(long testId, String key, int interval) {
		File reportDataFile = getReportDataFile(testId, key);
		return getFileDataAsList(reportDataFile, interval);
	}
Get json string that contains test report data as a json string.

@param testId   test id
@param key      key
@param interval interval to collect data
@return json list
ngrinder-controller/src/main/java/org/ngrinder/perftest/service/PerfTestService.java