@Test
  public void testEmptyMonitorContext()
      throws MeasurementNotAvailableException, InvalidMonitorContextException {
    MonitorContextBuilder builder = DefaultMonitorContext.builder();
    sensor.setMonitorContext(builder.build());

    System.out.println(sensor.getMeasurement().getValue());
  }
  @Test(expected = MeasurementNotAvailableException.class)
  public void testWrongFsRoot()
      throws MeasurementNotAvailableException, InvalidMonitorContextException {
    MonitorContextBuilder builder = DefaultMonitorContext.builder();
    builder.addContext("fs_root", "foobar");
    sensor.setMonitorContext(builder.build());

    System.out.println(sensor.getMeasurement().getValue());
  }
  @Test
  public void testFreeDiskSpaceSensor()
      throws InvalidMonitorContextException, MeasurementNotAvailableException, SigarException {
    MonitorContextBuilder builder = DefaultMonitorContext.builder();
    builder.addContext("fs_root", "/");
    builder.addContext("unit", "mb");
    sensor.setMonitorContext(builder.build());

    System.out.println(sensor.getMeasurement().getValue());
  }