单元测试不可测试那些类（无抽象、静态类、静态方法）

实际上“单元测试不可测试那些类（无抽象、静态类、静态方法）”是个伪命题，因为事实是：无抽象、静态类、静态方法都是不可单元测试的。那么，如果我们要写出可测试的代码，又要用到这些静态类等，该怎么办，实际上我们需要两个步骤：

1：为它们写一个包装类，让这个包装类是抽象的（继承自接口，或者抽象类，或者方法本身是Virtual的）；

2：通知客户端程序员，使用包装类来代替原先的静态类来写业务逻辑；

实际上，微软也是这么干的，我在上一篇博文《单元测试WebForm的UI逻辑及文件上传》写到，最典型的不可测试类，那就是WebForm架构的网站中，对Response等的模拟。查看Response这个类：

namespace System.Web
{
public sealed class HttpResponse
{
...
}
}

很明显，如果我们在某个WebForm的后台方法中，直接使用它的话：

protected void Page_Load(object sender, EvengArgs e)
{
this.Response.Write("test u");
}

该后台代码逻辑就无法进行单元测试了，因为类似MOQ的框架所依赖的是代码本身具有可被重写行，如果某个类本身是静态的，就无法在运行时用模拟类替换掉实际类。

所以，写一个包装类吧，我们看到微软为Response写了一个包装类，为HttpResponseWrapper：




View Code

namespace System.Web
{
[TypeForwardedFrom("System.Web.Abstractions, Version=3.5.0.0, Culture=Neutral, PublicKeyToken=31bf3856ad364e35")]
public class HttpResponseWrapper : HttpResponseBase
{
public override bool Buffer
{
get
{
}
set
{
}
}
public override bool BufferOutput
{
get
{
}
set
{
}
}
public override HttpCachePolicyBase Cache
{
get
{
}
}
public override string CacheControl
{
get
{
}
set
{
}
}
public override string Charset
{
get
{
}
set
{
}
}
public override CancellationToken ClientDisconnectedToken
{
get
{
}
}
public override Encoding ContentEncoding
{
get
{
}
set
{
}
}
public override string ContentType
{
get
{
}
set
{
}
}
public override HttpCookieCollection Cookies
{
get
{
}
}
public override int Expires
{
get
{
}
set
{
}
}
public override DateTime ExpiresAbsolute
{
get
{
}
set
{
}
}
public override Stream Filter
{
get
{
}
set
{
}
}
public override NameValueCollection Headers
{
get
{
}
}
public override Encoding HeaderEncoding
{
get
{
}
set
{
}
}
public override bool IsClientConnected
{
get
{
}
}
public override bool IsRequestBeingRedirected
{
get
{
}
}
public override TextWriter Output
{
get
{
}
set
{
}
}
public override Stream OutputStream
{
get
{
}
}
public override string RedirectLocation
{
get
{
}
set
{
}
}
public override string Status
{
get
{
}
set
{
}
}
public override int StatusCode
{
get
{
}
set
{
}
}
public override string StatusDescription
{
get
{
}
set
{
}
}
public override int SubStatusCode
{
get
{
}
set
{
}
}
public override bool SupportsAsyncFlush
{
get
{
}
}
public override bool SuppressContent
{
get
{
}
set
{
}
}
public override bool SuppressFormsAuthenticationRedirect
{
get
{
}
set
{
}
}
public override bool TrySkipIisCustomErrors
{
get
{
}
set
{
}
}
public HttpResponseWrapper(HttpResponse httpResponse)
{
}
public override void AddCacheItemDependency(string cacheKey)
{
}
public override void AddCacheItemDependencies(ArrayList cacheKeys)
{
}
public override void AddCacheItemDependencies(string[] cacheKeys)
{
}
public override void AddCacheDependency(params CacheDependency[] dependencies)
{
}
public override void AddFileDependency(string filename)
{
}
public override void AddFileDependencies(ArrayList filenames)
{
}
public override void AddFileDependencies(string[] filenames)
{
}
public override void AddHeader(string name, string value)
{
}
public override void AppendCookie(HttpCookie cookie)
{
}
public override void AppendHeader(string name, string value)
{
}
public override void AppendToLog(string param)
{
}
public override string ApplyAppPathModifier(string virtualPath)
{
}
public override IAsyncResult BeginFlush(AsyncCallback callback, object state)
{
}
public override void BinaryWrite(byte[] buffer)
{
}
public override void Clear()
{
}
public override void ClearContent()
{
}
public override void ClearHeaders()
{
}
public override void Close()
{
}
public override void DisableKernelCache()
{
}
public override void DisableUserCache()
{
}
public override void End()
{
}
public override void EndFlush(IAsyncResult asyncResult)
{
}
public override void Flush()
{
}
public override void Pics(string value)
{
}
public override void Redirect(string url)
{
}
public override void Redirect(string url, bool endResponse)
{
}
public override void RedirectPermanent(string url)
{
}
public override void RedirectPermanent(string url, bool endResponse)
{
}
public override void RedirectToRoute(object routeValues)
{
}
public override void RedirectToRoute(string routeName)
{
}
public override void RedirectToRoute(RouteValueDictionary routeValues)
{
}
public override void RedirectToRoute(string routeName, object routeValues)
{
}
public override void RedirectToRoute(string routeName, RouteValueDictionary routeValues)
{
}
public override void RedirectToRoutePermanent(object routeValues)
{
}
public override void RedirectToRoutePermanent(string routeName)
{
}
public override void RedirectToRoutePermanent(RouteValueDictionary routeValues)
{
}
public override void RedirectToRoutePermanent(string routeName, object routeValues)
{
}
public override void RedirectToRoutePermanent(string routeName, RouteValueDictionary routeValues)
{
}
public override void RemoveOutputCacheItem(string path)
{
}
public override void RemoveOutputCacheItem(string path, string providerName)
{
}
public override void SetCookie(HttpCookie cookie)
{
}
public override void TransmitFile(string filename)
{
}
public override void TransmitFile(string filename, long offset, long length)
{
}
public override void Write(string s)
{
}
public override void Write(char ch)
{
}
public override void Write(char[] buffer, int index, int count)
{
}
public override void Write(object obj)
{
}
public override void WriteFile(string filename)
{
}
public override void WriteFile(string filename, bool readIntoMemory)
{
}
public override void WriteFile(string filename, long offset, long size)
{
}
public override void WriteFile(IntPtr fileHandle, long offset, long size)
{
}
public override void WriteSubstitution(HttpResponseSubstitutionCallback callback)
{
}
}
}

光从代码本身的角度来说，可以说这个类什么事情也没做，但是它为我们提供了一个抽象体系（从抽象类HttpResponseBase继承），这样的话，我们的客户端代码就可以改写为：

protected HttpResponseBase _response;

protected void Page_Load(object sender, EvengArgs e)
{
_response.Write("test u");
}

OK，可测试了，因为我们可以在某个地方注入依赖给_response了。

注意，包装类的撰写，还可以使用接口，或者干脆也仅仅只是一个类，只要让被包装的这个同名的方法是virtual的就可以了。

另外，不可测试的那些类，可能往往已经作为稳定版本提交给客户了，我们就不能修改源代码然后告诉客户说你替换下我们的DLL吧，所以，为了让客户端程序员找到我们的包装类，可以让包装类以及被包装的类使用同一个命名空间。