在AutoFixture ISpecimenBuilder中使用RegEx時，爲什麼總是返回相同的值？

Question

我的構建器設置爲處理參數或屬性。這可能會改變未來，但現在這是我在我的建設者：

public class UserNameBuilder : ISpecimenBuilder 
{ 
    public object Create(object request, ISpecimenContext context) 
    { 
     var propertyInfo = request as PropertyInfo; 
     if (propertyInfo != null && propertyInfo.Name == "UserName" && propertyInfo.PropertyType == typeof(string)) 
     { 
      return GetUserName(); 
     } 

     var parameterInfo = request as ParameterInfo; 
     if (parameterInfo != null && parameterInfo.Name == "userName" && parameterInfo.ParameterType == typeof(string)) 
     { 
      return GetUserName(); 
     } 

     return new NoSpecimen(request); 
    } 

    static object GetUserName() 
    { 
     var fixture = new Fixture(); 
     return new SpecimenContext(fixture).Resolve(new RegularExpressionRequest(@"^[a-zA-Z0-9_.]{6,30}$")); 
    } 
} 

我的用戶名對象是值類型對象，如下所示：

public class UserName : SemanticType<string> 
{ 
    private static readonly Regex ValidPattern = new Regex(@"^[a-zA-Z0-9_.]{6,30}$"); 

    public UserName(string userName) : base(IsValid, userName) 
    { 
     Guard.NotNull(() => userName, userName); 
     Guard.IsValid(() => userName, userName, IsValid, "Invalid username"); 
    } 

    public static bool IsValid(string candidate) 
    { 
     return ValidPattern.IsMatch(candidate); 
    } 

    public static bool TryParse(string candidate, out UserName userName) 
    { 
     userName = null; 

     try 
     { 
      userName = new UserName(candidate); 
      return true; 
     } 
     catch (ArgumentException ex) 
     { 
      return false; 
     } 
    } 
} 

用戶名類繼承自SemanticType是爲我的值類型提供基礎的項目。

每當我使用AutoFixture如下：

var fixture = new Fixture(); 
fixture.Customizations.Add(new UserNameBuilder()); 

var userName = fixture.Create<UserName>(); 

我總是得到值「......」我想每一次我會得到不同的值。我看到預期的行爲？

Answer 1

如果可能的話，favor negated character classes instead of the dot，並嘗試use the dot sparingly：

^([a-zA-Z0-9]|[._](?![.])){6,30}$ 

上述正則表達式匹配也得到由最初的一個問題提供，例如匹配的文本nik_s.bax_vanis。

這也使得AutoFixture產生不同的文本以及（原諒我的F＃）：

// PM> Install-Package Unquote 
// PM> Install-Package AutoFixture 
// PM> Install-Package FsCheck.Xunit 

open FsCheck 
open FsCheck.Xunit 
open Ploeh.AutoFixture 
open Ploeh.AutoFixture.Kernel 
open Swensen.Unquote 

[<Property>] 
let ``Generated strings from RegEx are not all the same`` (PositiveInt count) = 
    let fixture = new Fixture() 
    let context = new SpecimenContext(fixture) 

    let results = seq { 
     for i in 1 .. count do 
      yield context.Resolve(
       new RegularExpressionRequest("^([a-zA-Z0-9]|[._](?![.])){6,30}$")) } 

    let threshold = count/10 
    results |> Seq.distinct |> Seq.length >! threshold 

---

原正則表達式是罰款。 - 這是引擎是重複dot多次地：

^[a-zA-Z0-9_.]{6,30}$