Sample code to run an in-memory HTTP context for unit testing in .NET

HttpTest.cs

internal class HttpTest
{
    private static HttpContext httpContext;
    private static HttpWorkerRequest httpWorkerRequest;
    private static StringBuilder outputStringBuilder;
    private static TextWriter output;
    private static NameValueCollection httpHeaders;
    private static HttpCookieCollection requestCookies;
    private static HttpCookieCollection responseCookies;

    public static HttpContext HttpContext
    {
        get { return httpContext; }
    }

    public static string Output
    {
        get { return outputStringBuilder.ToString(); }
    }

    public static void AddAjaxRequestHeader()
    {
        AddHttpHeader("X-Requested-With", "XMLHttpRequest");
    }

    public static void AddHttpHeader(string name, string value)
    {
        if (httpHeaders == null)
        {
            httpHeaders = new NameValueCollection();
        }
        httpHeaders.Add(name, value);
    }

    public static void DestroyHttpContext()
    {
        HttpContext.Current = null;
        httpHeaders = null;
        requestCookies = null;
        responseCookies = null;
    }

    public static void SetUpHttpContext(string page = "/default.aspx")
    {
        BuildResponseOutput();
        BuildHttpWorkerRequest(page);
        BuildHttpContext();
        BuildHttpSession();
    }

    private static void BuildHttpContext()
    {
        httpContext = new HttpContext(httpWorkerRequest);
        HttpContext.Current = httpContext;
    }

    private static void BuildHttpSession()
    {
        HttpContext.Current.SetSessionStateBehavior(SessionStateBehavior.Required);
        var sessionStateContainer = new HttpSessionStateContainer(Guid.NewGuid().ToString(), new SessionStateItemCollection(), new HttpStaticObjectsCollection(), 20000, true, HttpCookieMode.UseCookies, SessionStateMode.Off, false);
        SessionStateUtility.AddHttpSessionStateToContext(httpContext, sessionStateContainer);
    }

    private static void BuildHttpWorkerRequest(string page)
    {
        const string appVirtualDir = "/";
        const string appPhysicalDir = @"c:\";
        string query = string.Empty;
        httpWorkerRequest = new SimpleWorkerRequest(appVirtualDir, appPhysicalDir, page, query, output);
    }

    private static void BuildResponseOutput()
    {
        outputStringBuilder = new StringBuilder();
        output = new StringWriter(outputStringBuilder);
    }
}