anchor.diff:      }
     }
     
  +  /// Test the constructors.
     void simpleIntervalCreation() {
       _createBasicExpressions(interval);
   
  
positive.code:     'Custom Function INTERVAL evaluation': cusFuncIntervalEval,
      'Custom Function VECTOR evaluation': cusFuncVectorEval,
      'Composite Function creation': compFunCreation,
      'Composite Function evaluation': compFunEval,
      'Expression and Function differentiation': deriveTest,
      'Expression and Function simplification': simplifyTest,
    };
  
    void initTests() {
  
negative.code:     expect(_hasMember(e6, n1), isTrue);
    }
  
    /// Test the convenience constructors (binary, auto-wrapping).
    void convenienceBinaryCreation() {
      // Test Expression creation with convenience constructors.
      List<BinaryOperator> binOps = [new Times('x', 2), 
  