在Xunit中使用FsCheck

目录

编写基于Property-based的单元测试
使用FsCheck编写Property-based测试
在Xunit中使用FsCheck
使用FsCheck编写Model-based测试-待续

不管是Xunit仍是Nunit都有额外的扩展用来编写FsCheck测试，以Xunit为例 ：

Install-Package FsCheck.Xunit -Version 2.13.0

不一样于普通的Xunit测试，通常的测试须要标记[Fact]，你须要使用[Property]标记FsCheck测试。给定一个函数:

private int Add(int x, int y)
{
    return x + y;
}

针对加法交换律编写一个Property-based测试:

[Property]
public bool Commutative(int x, int y)
{
    return Add(x, y) == Add(y, x);
}

F#

[<Property>]
let Commutative x y =
    add x y = add y x

在以前的例子里，咱们介绍了什么是Property-based测试，而后花了一篇博客介绍了各类各样的Generator，每个刚开始了解Property-based测试的人都会以为这种方案颇有意思，可是当你真正开始编写Property-base测试的时候你就会感受得无从下手，应该断言什么样的Properties呢？
这篇文章介绍一些Properties供你参考:

1. 不一样的执行顺序，一样的执行结果

例如被测函数为List.OrderBy，若是咱们在List.OrderBy函数以前执行一个操做Add1，而后执行List.OrderBy函数。结果应该等于先执行List.OrderBy函数再执行操做Add1

[Property]
public bool AddOneThenSortShouldSameAsSortThenAddOne(List<int> list)
{
    var result1 = list.OrderBy(x => x).Select(Add1);
    var result2 = list.Select(Add1).OrderBy(x => x);

    return result1.SequenceEqual(result2);
}

F#

[<Property(Verbose=true)>]
let ``+1 then sort should be same as sort then +1`` aList =
    let add1 x = x + 1
    
    let result1 = aList |> List.sort |> List.map add1
    let result2 = aList |> List.map add1 |> List.sort
    
    result1 = result2

2.连续执行操做，结果跟以前一致

例如List.Reverse函数，连续执行两次，结果跟期初是同样的。相似的函数如序列化和反序列化，Redo和Undo。

[Property]
public bool ReverseThenReverseShouldSameAsOriginal(int[] list)
{
  var result=  list.Reverse().Reverse();
  return result.SequenceEqual(list);
}

F#

[<Property>]
let ``reverse then reverse should be same as original`` 
(aList:int list) =
    let reverseThenReverse = aList |> List.rev |> List.rev
    reverseThenReverse = aList

3. 有一些属性是永远不会改变的

在数据变化过程当中，有一些属性是永远不会改变的，例如Sort操做，先后数据的Length老是不变的，这一属性能够做为Property-based测试的一个依据:

public bool SomethingNeverChanged(List<int> list)
{
    var result = list.OrderBy(x => x);
    return result.Count() == list.Count;
}

F#

let ``sort should have same length as original`` (aList:int list) =
    let sorted = aList |> List.sort 
    List.length sorted = List.length aList

为OO代码编写Property-based测试

接下来咱们尝试针对一个OO的例子编写Property-based测试:

public class Dollar
{
    private int _amount;

    public Dollar(int amount)
    {
        _amount = amount;
    } 
    
    public int Amount => _amount;
    
    public void Add(int add)
    {
         _amount = _amount + add;
    }
    
    public void Multiplier(int multiplier)
    {
        _amount = _amount * multiplier;
    }
    
    public static Dollar Create(int amount)
    {
        return new Dollar(amount);
    }
}

F#

type Dollar(amount : int) =
    let mutable privateAmount = amount;

    member this.Amount = privateAmount
    member this.Add add =
        privateAmount <- this.Amount + add
    member this.Times multiplier =
        privateAmount <- this.Amount * multiplier
    static member Create amount =
        Dollar amount

Dollar类主要有两个方法，Add和Multiplier分别用来修改私有变量_amount。如何测试Dollar类呢？都有哪些Properties可用？调用Add方法后再读取Amount的值应该是同一个值：

[Property]
public bool SetAndGetShouldGiveSameResult(int amount)
{
    var dollar = Dollar.Create(0);
    dollar.Add(amount);

    return dollar.Amount == amount;
}

F#

[<Property>]
let ``set then get should give same result`` value =
    let obj = Dollar.Create 0
    obj.Add value
    let newValue = obj.Amount
    value = newValue

还有什么Property可供使用呢，Add和Multiplier两个方法执行完毕的结果等价于直接Create:

[Property]
public bool AddThenMultiplierSameAsCreate(int start, int times)
{
    var dollar = Dollar.Create(0);
    dollar.Add(start);
    dollar.Multiplier(times);

    var dollar2 = Dollar.Create(start * times);

    return dollar.Amount == dollar2.Amount;
}

F#

[<Property>]
let ``add then multiplier same as create`` value times =
    let dollar = Dollar.Create 0
    dollar.Add value
    dollar.Times times
    
    let dollar2 = Dollar.Create(value*times);
    
    dollar.Amount = dollar2.Amount

编写自定义Generator

迄今为止，咱们都在使用FsCheck自带的Generator，而在实际项目开发过程当中，你还须要生成自定义的Generator供你使用，例若有一个User类型：

public class User
{
    public string Name { get; set; }
    
    public int Age { get; set; }
}

自定义Generator:

public class UserArbitrary: Arbitrary<User>
{
    public override Gen<User> Generator =>
        from x in Arb.Generate<string>()
        from int y in Gen.Choose(20, 30)
        where x != string.Empty
        select new User {Name = x, Age = y};
}

最后还要将自定义的Arbitrary注册在FsCheck中：

public class MyGenerators {
    public static Arbitrary<User> User() {
        return new UserArbitrary();
    }
}

Arb.Register<MyGenerators>();

写个例子试试：

[Property]
public bool GenerateUsers(User user)
{
   return user.Name != string.Empty;
}

因此代码实例都可以在github下载