@Before
 public void setUp() throws Exception {
   CustomFeatureExtractor customFeatureExtractor = new CustomFeatureExtractor("testFeature", "0");
   customFeatureExtractor.setMeanExtractor(new MeanExtractor());
   customFeatureExtractor.setStdExtractor(new StdExtractor());
   featureExtractor = customFeatureExtractor;
 }
 private void setCustomFeatureExpression(String expression) {
   CustomFeatureExtractor customFeatureExtractor = (CustomFeatureExtractor) featureExtractor;
   customFeatureExtractor.setExpression(expression);
 }