Mock翻譯為“嘲弄”，其實就是偽造一個對象用於測試。在單元測試中，被測試方法依賴於其他對象時，為了測試簡單一般“偽造”一個這個對象；這樣做的目的：

• 不用考慮依賴對象的復雜性（方便準備測試數據）

• 只專註測試被測試方法，不將單元測試擴充到測試依賴對象

  打折算法測試

  商場中的商品類：
  

    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);
    }

被測試的打折算法

    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));
        }
 

顯然，被測試方法ValueProducts依賴打折接口IDiscountHelper,這裏通過偽造一個實現IDiscountHelper接口的對象。

Moq功能介紹

1. 創建偽造對象
   Mock<IDiscountHelper> mock = new Mock<IDiscountHelper>();
   
2. 設置偽造對象的方法
   mock.Setup(m => m.ApplyDiscount(It.IsAny<decimal>()))
   

3. 參數限制
   t.IsAny<decimal>()通過It限制這裏列出幾個

   限制表達式	解釋	例子
   It.Is	通過predicate返回bool值判斷限制測試	It.Is<decimal>(v => v == 0)
   It.IsAny	T類型的任意值	It.IsAny()
   It.IsInRange	T類型參數的值在範圍內或外(rangeKind參數決定)	It.IsInRange<int>(1, 100, Range.Inclusive)

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

構造單元測試

    [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));
        }
    }

單元測試之Mock(Moq)