单元测试之Mock(Moq)

Mock翻译为“嘲弄”，其实就是伪造一个对象用于测试。在单元测试中，被测试方法依赖于其他对象时，为了测试简单一般“伪造”一个这个对象；这样做的目的：

• 不用考虑依赖对象的复杂性（方便准备测试数据）

• 只专注测试被测试方法，不将单元测试扩充到测试依赖对象

  打折算法测试

  商场中的商品类：
  

    public class Product {
        public int ProductID { get; set; }
        public string Name { get; set; }
        public string Description { get; set; }
        public decimal Price { get; set; }
        public string Category { set; get; }
    }

打折接口：

    public interface IDiscountHelper {
        decimal ApplyDiscount(decimal totalParam);
    }

被测试的打折算法

    public class LinqValueCalculator : IValueCalculator {
        private IDiscountHelper discounter;

        public LinqValueCalculator(IDiscountHelper discountParam) {
            discounter = discountParam;
        }

        public decimal ValueProducts(IEnumerable<Product> products) {
            return discounter.ApplyDiscount(products.Sum(p => p.Price));
        }

显然，被测试方法ValueProducts依赖打折接口IDiscountHelper,这里通过伪造一个实现IDiscountHelper接口的对象。

Moq功能介绍

1. 创建伪造对象
   Mock<IDiscountHelper> mock = new Mock<IDiscountHelper>();
   
2. 设置伪造对象的方法
   mock.Setup(m => m.ApplyDiscount(It.IsAny<decimal>()))
   

3. 参数限制
   t.IsAny<decimal>()通过It限制这里列出几个

   限制表达式	解释	例子
   It.Is	通过predicate返回bool值判断限制测试	It.Is<decimal>(v => v == 0)
   It.IsAny	T类型的任意值	It.IsAny()
   It.IsInRange	T类型参数的值在范围内或外(rangeKind参数决定)	It.IsInRange<int>(1, 100, Range.Inclusive)

4. 设置返回值
   .Returns<decimal>(total => total);

构造单元测试

    [TestClass]
    public class UnitTest2 {

        private Product[] createProduct(decimal value) {
            return new[] { new Product { Price = value } };
        }

        [TestMethod]
        [ExpectedException(typeof(System.ArgumentOutOfRangeException))]
        public void Pass_Through_Variable_Discounts() {
            // arrange
            Mock<IDiscountHelper> mock = new Mock<IDiscountHelper>();
            mock.Setup(m => m.ApplyDiscount(It.IsAny<decimal>()))
                .Returns<decimal>(total => total);
            mock.Setup(m => m.ApplyDiscount(It.Is<decimal>(v => v == 0)))
                .Throws<System.ArgumentOutOfRangeException>();
            mock.Setup(m => m.ApplyDiscount(It.Is<decimal>(v => v > 100)))
                .Returns<decimal>(total => (total * 0.9M));
            mock.Setup(m => m.ApplyDiscount(It.IsInRange<decimal>(10, 100,
                Range.Inclusive))).Returns<decimal>(total => total - 5);
            var target = new LinqValueCalculator(mock.Object);

            // act
            decimal FiveDollarDiscount = target.ValueProducts(createProduct(5));
            decimal TenDollarDiscount = target.ValueProducts(createProduct(10));
            decimal FiftyDollarDiscount = target.ValueProducts(createProduct(50));
            decimal HundredDollarDiscount = target.ValueProducts(createProduct(100));
            decimal FiveHundredDollarDiscount = target.ValueProducts(createProduct(500));

            // assert
            Assert.AreEqual(5, FiveDollarDiscount, "$5 Fail");
            Assert.AreEqual(5, TenDollarDiscount, "$10 Fail");
            Assert.AreEqual(45, FiftyDollarDiscount, "$50 Fail");
            Assert.AreEqual(95, HundredDollarDiscount, "$100 Fail");
            Assert.AreEqual(450, FiveHundredDollarDiscount, "$500 Fail");
            target.ValueProducts(createProduct(0));
        }
    }