public void GetIdentifier_ExistingSession_NotNull()
        {
            var ctxt = new DefaultHttpContext();
            var session = Subject.Initialize(ctxt);

            Assert.Equal(session, Subject.GetIdentifier(ctxt));
        }

        public async Task Create_InstanceNotNull()
        {
            var ctxt = new DefaultHttpContext();

            var session = await CreateNew(ctxt, "Test");
            Assert.NotNull(session.Instance);
        }

        public void CopyConstructor_CopiesExpectedProperties()
        {
            // Arrange
            var httpContext = new DefaultHttpContext();
            var originalContext = new ViewContext(
                new ActionContext(httpContext, new RouteData(), new ActionDescriptor()),
                view: Mock.Of<IView>(),
                viewData: new ViewDataDictionary(metadataProvider: new EmptyModelMetadataProvider()),
                tempData: new TempDataDictionary(httpContext, Mock.Of<ITempDataProvider>()),
                writer: TextWriter.Null,
                htmlHelperOptions: new HtmlHelperOptions());
            var view = Mock.Of<IView>();
            var viewData = new ViewDataDictionary(originalContext.ViewData);
            var writer = new HtmlContentWrapperTextWriter(new HtmlContentBuilder(), Encoding.UTF8);

            // Act
            var context = new ViewContext(originalContext, view, viewData, writer);

            // Assert
            Assert.Same(originalContext.ActionDescriptor, context.ActionDescriptor);
            Assert.Equal(originalContext.ClientValidationEnabled, context.ClientValidationEnabled);
            Assert.Same(originalContext.ExecutingFilePath, context.ExecutingFilePath);
            Assert.Same(originalContext.FormContext, context.FormContext);
            Assert.Equal(originalContext.Html5DateRenderingMode, context.Html5DateRenderingMode);
            Assert.Same(originalContext.HttpContext, context.HttpContext);
            Assert.Same(originalContext.ModelState, context.ModelState);
            Assert.Same(originalContext.RouteData, context.RouteData);
            Assert.Same(originalContext.TempData, context.TempData);
            Assert.Same(originalContext.ValidationMessageElement, context.ValidationMessageElement);
            Assert.Same(originalContext.ValidationSummaryMessageElement, context.ValidationSummaryMessageElement);

            Assert.Same(view, context.View);
            Assert.Same(viewData, context.ViewData);
            Assert.Same(writer, context.Writer);
        }

        public void Initialize_SessionHeaderCreated()
        {
            var ctxt = new DefaultHttpContext();
            var session = Subject.Initialize(ctxt);

            Assert.Equal(session, ctxt.Response.Headers[Options.SessionHeader]);
        }

        public static HttpContextAccessor CreateHttpContextAccessor(RequestTelemetry requestTelemetry = null, ActionContext actionContext = null)
        {
            var services = new ServiceCollection();

            var request = new DefaultHttpContext().Request;
            request.Method = "GET";
            request.Path = new PathString("/Test");
            var contextAccessor = new HttpContextAccessor() { HttpContext = request.HttpContext };

            services.AddInstance<IHttpContextAccessor>(contextAccessor);

            if (actionContext != null)
            {
                var si = new ActionContextAccessor();
                si.ActionContext = actionContext;
                services.AddInstance<IActionContextAccessor>(si);
            }

            if (requestTelemetry != null)
            {
                services.AddInstance<RequestTelemetry>(requestTelemetry);
            }

            IServiceProvider serviceProvider = services.BuildServiceProvider();
            contextAccessor.HttpContext.RequestServices = serviceProvider;

            return contextAccessor;
        }

        public void SettingViewData_AlsoUpdatesViewBag()
        {
            // Arrange
            var httpContext = new DefaultHttpContext();
            var originalViewData = new ViewDataDictionary(metadataProvider: new EmptyModelMetadataProvider());
            var context = new ViewContext(
                new ActionContext(new DefaultHttpContext(), new RouteData(), new ActionDescriptor()),
                view: Mock.Of<IView>(),
                viewData: originalViewData,
                tempData: new TempDataDictionary(httpContext, Mock.Of<ITempDataProvider>()),
                writer: TextWriter.Null,
                htmlHelperOptions: new HtmlHelperOptions());
            var replacementViewData = new ViewDataDictionary(metadataProvider: new EmptyModelMetadataProvider());

            // Act
            context.ViewBag.Hello = "goodbye";
            context.ViewData = replacementViewData;
            context.ViewBag.Another = "property";

            // Assert
            Assert.NotSame(originalViewData, context.ViewData);
            Assert.Same(replacementViewData, context.ViewData);
            Assert.Null(context.ViewBag.Hello);
            Assert.Equal("property", context.ViewBag.Another);
            Assert.Equal("property", context.ViewData["Another"]);
        }

        public void Clear_AlreadyStarted_Throws()
        {
            var context = new DefaultHttpContext();
            context.Features.Set<IHttpResponseFeature>(new StartedResponseFeature());

            Assert.Throws<InvalidOperationException>(() => context.Response.Clear());
        }

        public void CanUseRegisterExtensionMethod()
        {
            var curie = new CuriesLink("aap", "http://www.helpt.com/{?rel}");

            var builder = Hypermedia.CreateBuilder();
            var selfLink = new Link<ProductRepresentation>("product", "http://www.product.com?id=1");
            var link2 = new Link("related", "http://www.related.com");
            var link3 = curie.CreateLink<CategoryRepresentation>("category", "http://www.category.com");

            builder.Register(selfLink, link2, link3);

            var config = builder.Build();

            // arrange
            var mediaFormatter = new JsonHalOutputFormatter(config) { };
            var type = representation.GetType();
            var httpContext = new Mock<HttpContext>();
            var httpRequest = new DefaultHttpContext().Request;
            httpContext.SetupGet(o => o.Request).Returns(httpRequest);

            // act
            using (var stream = new MemoryStream())
            {
                mediaFormatter.WriteResponseBodyAsync(new OutputFormatterWriteContext(httpContext.Object,
                    (s,e)=> new HttpResponseStreamWriter(s, e), type, representation));
                //WriteToStreamAsync(type, representation, stream, content, null);
                stream.Seek(0, SeekOrigin.Begin);
                var serialisedResult = new StreamReader(stream).ReadToEnd();

                // assert
                Approvals.Verify(serialisedResult);
            }
        }

        public async Task WriteFileAsync_WritesResponse_InChunksOfFourKilobytes()
        {
            // Arrange
            var mockReadStream = new Mock<Stream>();
            mockReadStream.SetupSequence(s => s.ReadAsync(It.IsAny<byte[]>(), 0, 0x1000, CancellationToken.None))
                .Returns(Task.FromResult(0x1000))
                .Returns(Task.FromResult(0x500))
                .Returns(Task.FromResult(0));

            var mockBodyStream = new Mock<Stream>();
            mockBodyStream
                .Setup(s => s.WriteAsync(It.IsAny<byte[]>(), 0, 0x1000, CancellationToken.None))
                .Returns(Task.FromResult(0));

            mockBodyStream
                .Setup(s => s.WriteAsync(It.IsAny<byte[]>(), 0, 0x500, CancellationToken.None))
                .Returns(Task.FromResult(0));

            var result = new FileStreamResult(mockReadStream.Object, "text/plain");

            var httpContext = new DefaultHttpContext();
            httpContext.Response.Body = mockBodyStream.Object;

            var actionContext = new ActionContext(httpContext, new RouteData(), new ActionDescriptor());

            // Act
            await result.ExecuteResultAsync(actionContext);

            // Assert
            mockReadStream.Verify();
            mockBodyStream.Verify();
        }

        public async Task WriteFileAsync_CopiesProvidedStream_ToOutputStream()
        {
            // Arrange
            // Generate an array of bytes with a predictable pattern
            // 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F, 10, 11, 12, 13
            var originalBytes = Enumerable.Range(0, 0x1234)
                .Select(b => (byte)(b % 20)).ToArray();

            var originalStream = new MemoryStream(originalBytes);

            var httpContext = new DefaultHttpContext();
            var outStream = new MemoryStream();
            httpContext.Response.Body = outStream;

            var actionContext = new ActionContext(httpContext, new RouteData(), new ActionDescriptor());

            var result = new FileStreamResult(originalStream, "text/plain");

            // Act
            await result.ExecuteResultAsync(actionContext);

            // Assert
            var outBytes = outStream.ToArray();
            Assert.True(originalBytes.SequenceEqual(outBytes));
        }

        public async void Invoke_DoesNotLog_WhenHandled()
        {
            // Arrange
            var isHandled = true;

            var sink = new TestSink(
                TestSink.EnableWithTypeName<RouterMiddleware>,
                TestSink.EnableWithTypeName<RouterMiddleware>);
            var loggerFactory = new TestLoggerFactory(sink, enabled: true);

            var httpContext = new DefaultHttpContext();
            httpContext.ApplicationServices = new ServiceProvider();
            httpContext.RequestServices = httpContext.ApplicationServices;

            RequestDelegate next = (c) =>
            {
                return Task.FromResult<object>(null);
            };

            var router = new TestRouter(isHandled);
            var middleware = new RouterMiddleware(next, loggerFactory, router);

            // Act
            await middleware.Invoke(httpContext);

            // Assert
            Assert.Empty(sink.Scopes);
            Assert.Empty(sink.Writes);
        }

        public async void Invoke_LogsCorrectValues_WhenNotHandled()
        {
            // Arrange
            var expectedMessage = "Request did not match any routes.";
            var isHandled = false;

            var sink = new TestSink(
                TestSink.EnableWithTypeName<RouterMiddleware>,
                TestSink.EnableWithTypeName<RouterMiddleware>);
            var loggerFactory = new TestLoggerFactory(sink, enabled: true);

            var httpContext = new DefaultHttpContext();
            httpContext.ApplicationServices = new ServiceProvider();
            httpContext.RequestServices = httpContext.ApplicationServices;

            RequestDelegate next = (c) =>
            {
                return Task.FromResult<object>(null);
            };

            var router = new TestRouter(isHandled);
            var middleware = new RouterMiddleware(next, loggerFactory, router);

            // Act
            await middleware.Invoke(httpContext);

            // Assert
            Assert.Empty(sink.Scopes);
            Assert.Single(sink.Writes);
            Assert.Equal(expectedMessage, sink.Writes[0].State?.ToString());
        }

        public void SelectResponseCharacterEncoding_SelectsEncoding(
            string acceptCharsetHeaders,
            string[] supportedEncodings,
            string expectedEncoding)
        {
            // Arrange
            var httpContext = new Mock<HttpContext>();
            var httpRequest = new DefaultHttpContext().Request;
            httpRequest.Headers[HeaderNames.AcceptCharset] = acceptCharsetHeaders;
            httpRequest.Headers[HeaderNames.Accept] = "application/acceptCharset";
            httpContext.SetupGet(o => o.Request).Returns(httpRequest);

            var formatter = new TestOutputFormatter();
            foreach (string supportedEncoding in supportedEncodings)
            {
                formatter.SupportedEncodings.Add(Encoding.GetEncoding(supportedEncoding));
            }

            var context = new OutputFormatterWriteContext(
                httpContext.Object,
                new TestHttpResponseStreamWriterFactory().CreateWriter,
                typeof(string),
                "someValue")
            {
                ContentType = MediaTypeHeaderValue.Parse(httpRequest.Headers[HeaderNames.Accept]),
            };

            // Act
            var actualEncoding = formatter.SelectCharacterEncoding(context);

            // Assert
            Assert.Equal(Encoding.GetEncoding(expectedEncoding), actualEncoding);
        }

        private static ViewComponentContext GetViewComponentContext(IView view, Stream stream)
        {
            var httpContext = new DefaultHttpContext();
            var actionContext = new ActionContext(httpContext, new RouteData(), new ActionDescriptor());
            var viewData = new ViewDataDictionary(new EmptyModelMetadataProvider());
            var viewContext = new ViewContext(
                actionContext,
                view,
                viewData,
                new TempDataDictionary(httpContext, new SessionStateTempDataProvider()),
                TextWriter.Null,
                new HtmlHelperOptions());

            var writer = new StreamWriter(stream) { AutoFlush = true };

            var viewComponentDescriptor = new ViewComponentDescriptor()
            {
                Type = typeof(object),
            };

            var viewComponentContext = new ViewComponentContext(
                viewComponentDescriptor,
                new Dictionary<string, object>(),
                new HtmlTestEncoder(),
                viewContext,
                writer);

            return viewComponentContext;
        }

        public async Task ReadFormAsync_SimpleData_ReturnsParsedFormCollection()
        {
            // Arrange
            var formContent = Encoding.UTF8.GetBytes("foo=bar&baz=2");
            var context = new DefaultHttpContext();
            context.Request.ContentType = "application/x-www-form-urlencoded; charset=utf-8";
            context.Request.Body = new MemoryStream(formContent);

            // Not cached yet
            var formFeature = context.Features.Get<IFormFeature>();
            Assert.Null(formFeature);

            // Act
            var formCollection = await context.Request.ReadFormAsync();

            // Assert
            Assert.Equal("bar", formCollection["foo"]);
            Assert.Equal("2", formCollection["baz"]);
            Assert.Equal(0, context.Request.Body.Position);
            Assert.True(context.Request.Body.CanSeek);

            // Cached
            formFeature = context.Features.Get<IFormFeature>();
            Assert.NotNull(formFeature);
            Assert.NotNull(formFeature.Form);
            Assert.Same(formFeature.Form, formCollection);
        }

        public async Task ExecuteResultAsync_FallsBackToThePhysicalFileProvider_IfNoFileProviderIsPresent()
        {
            // Arrange
            var path = Path.Combine("TestFiles", "FilePathResultTestFile.txt");
            var result = new FilePathResult(path, "text/plain");

            var appEnvironment = new Mock<IHostingEnvironment>();
            appEnvironment.Setup(app => app.WebRootFileProvider)
                .Returns(new PhysicalFileProvider(Directory.GetCurrentDirectory()));

            var httpContext = new DefaultHttpContext();
            httpContext.Response.Body = new MemoryStream();
            httpContext.RequestServices = new ServiceCollection()
                .AddInstance<IHostingEnvironment>(appEnvironment.Object)
                .BuildServiceProvider();

            var context = new ActionContext(httpContext, new RouteData(), new ActionDescriptor());

            // Act
            await result.ExecuteResultAsync(context);
            httpContext.Response.Body.Position = 0;

            // Assert
            Assert.NotNull(httpContext.Response.Body);
            var contents = await new StreamReader(httpContext.Response.Body).ReadToEndAsync();
            Assert.Equal("FilePathResultTestFile contents", contents);
        }

        public TestBase()
        {
            if (ServiceProvider == null)
            {
                var services = new ServiceCollection();

                // set up empty in-memory test db
                services.AddEntityFramework()
                    .AddInMemoryDatabase()
                    .AddDbContext<AllReadyContext>(options => options.UseInMemoryDatabase());

                // add identity service
                services.AddIdentity<ApplicationUser, IdentityRole>()
                    .AddEntityFrameworkStores<AllReadyContext>();
                var context = new DefaultHttpContext();
                context.Features.Set<IHttpAuthenticationFeature>(new HttpAuthenticationFeature());
                services.AddSingleton<IHttpContextAccessor>(h => new HttpContextAccessor { HttpContext = context });

                // Setup hosting environment
                IHostingEnvironment hostingEnvironment = new HostingEnvironment();
                hostingEnvironment.EnvironmentName = "Development";
                services.AddSingleton(x => hostingEnvironment);

                // set up service provider for tests
                ServiceProvider = services.BuildServiceProvider();
            }
        }

        public Task ExpectedKeysAreAvailable()
        {
            var handler = new ClientHandler(env =>
            {
                var context = new DefaultHttpContext((IFeatureCollection)env);

                // TODO: Assert.True(context.RequestAborted.CanBeCanceled);
                Assert.Equal("HTTP/1.1", context.Request.Protocol);
                Assert.Equal("GET", context.Request.Method);
                Assert.Equal("https", context.Request.Scheme);
                Assert.Equal("/A/Path", context.Request.PathBase.Value);
                Assert.Equal("/and/file.txt", context.Request.Path.Value);
                Assert.Equal("?and=query", context.Request.QueryString.Value);
                Assert.NotNull(context.Request.Body);
                Assert.NotNull(context.Request.Headers);
                Assert.NotNull(context.Response.Headers);
                Assert.NotNull(context.Response.Body);
                Assert.Equal(200, context.Response.StatusCode);
                Assert.Null(context.Features.Get<IHttpResponseFeature>().ReasonPhrase);
                Assert.Equal("example.com", context.Request.Host.Value);

                return Task.FromResult(0);
            }, new PathString("/A/Path/"));
            var httpClient = new HttpClient(handler);
            return httpClient.GetAsync("https://example.com/A/Path/and/file.txt?and=query");
        }

        public async Task Index_ReturnsNoCartItems_WhenNoItemsInCart()
        {
            // Arrange
            var httpContext = new DefaultHttpContext();
            httpContext.Session = new TestSession();
            httpContext.Session.SetString("Session", "CartId_A");

            var controller = new ShoppingCartController()
            {
                DbContext = _serviceProvider.GetRequiredService<MusicStoreContext>(),
            };
            controller.ActionContext.HttpContext = httpContext;

            // Act
            var result = await controller.Index();

            // Assert
            var viewResult = Assert.IsType<ViewResult>(result);
            Assert.NotNull(viewResult.ViewData);
            Assert.Null(viewResult.ViewName);

            var model = Assert.IsType<ShoppingCartViewModel>(viewResult.ViewData.Model);
            Assert.Equal(0, model.CartItems.Count);
            Assert.Equal(0, model.CartTotal);
        }

        public void EmptyUserIsNeverNull()
        {
            var context = new DefaultHttpContext(new FeatureCollection());
            Assert.NotNull(context.User);
            Assert.Equal(1, context.User.Identities.Count());
            Assert.True(object.ReferenceEquals(context.User, context.User));
            Assert.False(context.User.Identity.IsAuthenticated);
            Assert.True(string.IsNullOrEmpty(context.User.Identity.AuthenticationType));

            context.User = null;
            Assert.NotNull(context.User);
            Assert.Equal(1, context.User.Identities.Count());
            Assert.True(object.ReferenceEquals(context.User, context.User));
            Assert.False(context.User.Identity.IsAuthenticated);
            Assert.True(string.IsNullOrEmpty(context.User.Identity.AuthenticationType));

            context.User = new ClaimsPrincipal();
            Assert.NotNull(context.User);
            Assert.Equal(0, context.User.Identities.Count());
            Assert.True(object.ReferenceEquals(context.User, context.User));
            Assert.Null(context.User.Identity);

            context.User = new ClaimsPrincipal(new ClaimsIdentity("SomeAuthType"));
            Assert.Equal("SomeAuthType", context.User.Identity.AuthenticationType);
            Assert.True(context.User.Identity.IsAuthenticated);
        }