anchor.diff:          [4.0, 0.0, 1.0],
         ]);
         final labels = Matrix.from([
  -        [0.0],
  -        [1.0],
  -        [1.0],
  -        [2.0],
  -        [0.0]
  +        firstClass,
  +        secondClass,
  +        secondClass,
  +        thirdClass,
  +        firstClass,
         ]);
         classifier.fit(features, labels);
   
  
positive.code: 
  void main() {
    LogisticRegressor classifier;
  
    group('Logistic regressor', () {
      setUp(() {
  
negative.code:         [1.0, 2.0, 3.0],
        ]);
        final labels = Matrix.from([
          [1.0, 0.0],
          [0.0, 1.0],
        ]);
        classifier.fit(features, labels);
  
  