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：
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。
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