anchor.diff:            null,
             splittingValues,
           );
  -        expect(stump, equals([
  +        expect(stump.observations, equals([
             [
               [11, 22, 0, 0, 1, 30],
               [60, 23, 0, 0, 1, 20],
  
positive.code:           null,
            splittingValues,
          );
          expect(stump, equals(<Matrix>[]));
        });
  
        test('should return an empty stump if no one value from the splitting'
  
negative.code:           null,
            splittingValues,
          );
          expect(stump.observations, equals([
            [
              [11, 22, 0, 0, 1, 30],
              [60, 23, 0, 0, 1, 20],
  