@Test
public void testParseTimeFormatNowPrecision() throws LogicalOperatorException {

  String timePrecision = IoTDBDescriptor.getInstance().getConfig().getTimestampPrecision();
  IoTDBDescriptor.getInstance().getConfig().setTimestampPrecision("ms");
  long now_ms = generator.parseTimeFormat(SQLConstant.NOW_FUNC);
  String ms_str = String.valueOf(now_ms);
  IoTDBDescriptor.getInstance().getConfig().setTimestampPrecision("us");
  long now_us = generator.parseTimeFormat(SQLConstant.NOW_FUNC);
  String us_str = String.valueOf(now_us);
  IoTDBDescriptor.getInstance().getConfig().setTimestampPrecision("ns");
  long now_ns = generator.parseTimeFormat(SQLConstant.NOW_FUNC);
  String ns_str = String.valueOf(now_ns);
  assertEquals(ms_str.length() + 3, (us_str).length());
  assertEquals(us_str.length() + 3, (ns_str).length());
  IoTDBDescriptor.getInstance().getConfig().setTimestampPrecision(timePrecision);
}