public void ExtensionNotSupportedTest()
        {
            // Tests that calling RenderPage on an unsupported extension returns a new simpler error message
            // instead of the full error about build providers in system.web.dll.
            var vpath = "~/hello/world.txt";
            var ext = ".txt";
            var compilationUtilThrowingBuildManager = new CompilationUtil();
            var otherExceptionBuildManager = new Mock<IVirtualPathFactory>();
            var msg = "The file \"~/hello/world.txt\" could not be rendered, because it does not exist or is not a valid page.";
            otherExceptionBuildManager.Setup(c => c.CreateInstance(It.IsAny<string>())).Throws(new HttpException(msg));

            Assert.Throws<HttpException>(() =>
                                                  WebPage.CreateInstanceFromVirtualPath(vpath, new VirtualPathFactoryManager(compilationUtilThrowingBuildManager)),
                                                  String.Format(CultureInfo.CurrentCulture, WebPageResources.WebPage_FileNotSupported, ext, vpath));

            // Test that other error messages are thrown unmodified.
            Assert.Throws<HttpException>(() => WebPage.CreateInstanceFromVirtualPath(vpath, otherExceptionBuildManager.Object), msg);
        }