public void Equals()
        {
            MultiplyExpression expr1 = new MultiplyExpression(new ConstantExpression(1), new ConstantExpression(2));
            MultiplyExpression expr2 = new MultiplyExpression(new ConstantExpression(1), new ConstantExpression(3));
            MultiplyExpression expr3 = new MultiplyExpression(new ConstantExpression(1), new ConstantExpression(2));
            MultiplyExpression expr4 = new MultiplyExpression(new ConstantExpression(2), new ConstantExpression(2));

            Assert.IsTrue(expr1.Equals(expr3));
            Assert.IsTrue(expr3.Equals(expr1));
            Assert.AreEqual(expr1.GetHashCode(), expr3.GetHashCode());

            Assert.IsFalse(expr1.Equals(null));
            Assert.IsFalse(expr1.Equals("foo"));
            Assert.IsFalse(expr1.Equals(expr2));
            Assert.IsFalse(expr2.Equals(expr1));
            Assert.IsFalse(expr1.Equals(expr4));
            Assert.IsFalse(expr4.Equals(expr1));
        }