Unit testing aspnet core 2.1

With the release of dotnet core 2.1, a lot of things came together. Things like signalr and dependency injection. No more fighting the version numbers. Trying to get the exact version of signalr to work with the other exact version of dotnet runtime and so on.

Now, when things settled down, let’s get testing to work.

In this this post, I make a note to self about how to mock enough stuff to make unit testing to work.

Project here


Here, I create three projects. The web, the definitions and the repository.
Ah, and the additional Test project.

So, fire up the good old command line and type

md demo
cd demo
dotnet new sln --name Demo
dotnet new mvc --name Demo.Web
dotnet new classlib --name Demo.Definitions
dotnet new classlib --name Demo.Repositories
dotnet new classlib --name Demo.Models
dotnet new xunit --name Demo.Tests

and now (if you are using Visual Studio 2017 proper) you would like to add them to the solution

dotnet sln add Demo.Web
dotnet sln add Demo.Definitions
dotnet sln add Demo.Repositories
dotnet sln add Demo.Tests
dotnet sln add Demo.Models

And don’t forget to reference Definitions from Repository and so on with

cd Demo.Web
dotnet add reference ..\Demo.Definitions\Demo.Definitions.csproj
dotnet add reference ..\Demo.Repositories\Demo.Repositories.csproj
cd ..\Demo.Repositories
dotnet add reference ..\Demo.Definitions\Demo.Definitions.csproj
dotnet add reference ..\Demo.Models\Demo.Models.csproj
cd ..\Demo.Models
dotnet add reference ..\Demo.Definitions\Demo.Definitions.csproj
cd ..\Demo.Tests
dotnet add reference ..\Demo.Definitions\Demo.Definitions.csproj
dotnet add reference ..\Demo.Models\Demo.Models.csproj
dotnet add reference ..\Demo.Repositories\Demo.Repositories.csproj
dotnet add reference ..\Demo.Web\Demo.Web.csproj

In this case I have a homecontroller that need the repository injected for data access and also need access to the signalr hub for push notifications to the web.

I’ll begin by creating the interfaces, models and repository.
Next, I’ll inject the repo in the HomeController. I’ll also inject the HubContext for the NotificationHub.

private readonly IRepository _repo = null;
IHubContext<NotificationHub> _hubContext = null;
public HomeController(IRepository repo, IHubContext<NotificationHub> hubContext)


For this to work we register the interface in the DI-container in Startup.cs

In the ConfigureServices method we add

services.AddTransient<IRepository, CustomerRepository>();
So, now it works and the customer Acme is shown when browsing /Home/Customer/1


For testing purposes I’ll use the DependencyInjection, FluentAssertions and Moq nuget packages.
cd Demo.Tests
dotnet add package Microsoft.Extensions.DependencyInjection -v 2.1.0
dotnet add package FluentAssertions
dotnet add package Moq

For easy access to signalR and other stuff that the web project use add also the same package the webapp is using Microsoft.AspNetCore.App

dotnet add package Microsoft.AspNetCore.App -v 2.1.0

DependencyInjection and aspnetcore are interdependent and need to be of the same version.

So, In my first test I need to mock the repository

var repo = new Mock<IRepository<ICustomer>>();
repo.Setup(x => x.GetById(1)).Returns(() =>
    return new Customer{Id = 1, CustomerName = "Acme", CreatedOn = DateTime.Now};

This means that when call GetById with parameter 1, the anonymous function sent as a parameter to Returns is executed.

Furthermore, in my HomeController action UpdateCustomer I’m executing a call to the signalr hub NotificationHub.

await _hubContext.Clients.All.SendAsync("ReceiveMessage", customer);

This has to be mocked in three steps. First a mock of _hubContext that is of type IHubcontext<NotificationHub> that, when the property Clients is requested, returns an IHubClients object. This, in turn, must mock its All property to return an IClientProxy.

Since they are referencing each other we have to mock them in reverse.

var mockClientProxy = new Mock<IClientProxy>();

var mockClients = new Mock<IHubClients>();
mockClients.Setup(clients => clients.All).Returns(mockClientProxy.Object);

var hub = new Mock<IHubContext<NotificationHub>>();
hub.Setup(x => x.Clients).Returns(() => mockClients.Object);

Then register these objects in the IoC container

var provider = new ServiceCollection()
    .AddSingleton <IRepository<ICustomer>> (repo.Object)
    .AddTransient<HomeController, HomeController>()

Now when I calls for my test subject, HomeController, The IoC container resolves the dependencies

var controller = provider.GetService<HomeController>();
As a bonus we can add some cookies if your controller need them
controller.ControllerContext.HttpContext = new DefaultHttpContext();
controller.ControllerContext.HttpContext.Request.Headers.Add("Cookie", "userid=mchammer;recordno=2");

Then just to the assert

var albumc = await controller.UpdateCustomer(customer);

This example is admittedly quite construed (I’m testing the mock 🙂 ) but serves the purpose to show the mocking of both a signalr hub internals and then stack them together plus injecting the dependencies into the container.

Stream error in the HTTP/2 framing layer

When using R for posting json to a web api I got the error

Error in curl::curl_fetch_memory(url, handle = handle) :
Stream error in the HTTP/2 framing layer

But only after the first successful run. Strange. Something was hanging the handle in the background. Or that was my guess at least.

Anyway, if I set the version back to HTTP/1.1 it works fine.

Here is the gist of it

Adding authentication in AspNetCore 2.0

<EDIT> A few days ago they changed it again….
Instead of .AddCookieAuthentication(….
It’s now just .AddCookie();

Or rather Aspnetcore 2.0.0-preview2-006497 since they changed it again….

First, download the latest bits from .NET Core 2.0 and install it.
Open a developer command prompt and check version with

dotnet –version

It should say 2.0.0-preview2-006497 for you to be sure that my instructions will work 🙂
Create a new folder for your project and create a new mvc project with

dotnet new mvc

After it is done we will add the dependencies for authentication

dotnet add package Microsoft.AspNetCore.Authentication -v “2.0.0-preview2-final”


dotnet add package Microsoft.AspNetCore.Http -v “2.0.0-preview2-final”

Now we add, one by one the authentication providers we want. In Startup.cs in ConfigureServices:

The biggest change in this version is perhaps that you only add


To the pipeline in the Configure method.

So. Done with that part. Oh, forgot the usings. Add these to the top

A few more than necessary but I will get to them. Now the project should start with

dotnet run

But it still allows for anonymous access.

Add the attribute [Authorize] to your HomeController together with a matching using like so:

So. Again start the project and browse to http://localhost:5000/. You will be redirected to /home/login and get an error since that page does not exist (yet).

In the HomeController.cs add this code

This is used when you manage all the users and passwords yourself (please don’t).
But seriously, sometimes you have an old back-end system that you are building a new front-web for and it has all the user info.

I created a super simplistic view for this action. Create a new file in the folder Views/Home called Login.cshtml with this content

Told you. Simplistic. Make sure these “usings” are in place in your HomeController.cs

Now, go back up to the project root folder and run the application again. This time the login page is displayed. If you try to login with your hard coded username and password you will be logged in and redirected to /. If you inspect the ClaimsPrincipal when debugging you will see that your claims are visible under the Identity-property.


Great. Let the user logout as well.

Add a link somewhere that redirects the user to /home/logout. Done.

So. How about Twitter?

First, add a new app at apps.twitter.com . Click “Create new app” and fill out the form. You can set callback url to localhost:5000. Go to the Keys and Access Tokens-tab and copy them to your appSettings.json file

Please note that if you intend to publish the code somewhere, don’t store these credentials here. Use secrets instead.

Remember the fancy looking login page? The Twitter-link was /login-twitter. Just because it is fun I will hard-wire this url into the processing pipeline.

So. Head over to Startup.cs and paste this code into the Configure-method.

Now you redirected to a Twitter page and depending if you are already logged into Twitter or not the page either asks you to logon or only to authorize your new app to connect to Twitter.

Tip: If you want to dress the current user with more claims than Twitter sent, you can always add them. Like your internal user id of that Twitter-identified user.

Code on Github


Xamarin: error APT0000: Error parsing XML: syntax error

This error had me hunting for two whole days. I couldn’t understand where the files Xamarin was complaining about. They were certainly not mine….

I noticed that when I backgraded to Xamarin.Forms v1.5.1.6471 the problem disappeared. After fiddling around desperately (as you do) a pattern emerged. The trick seemed to be to not reference the support libraries Xamarin.Android.Support.* that had versions >

As soon as they were referenced, the build crashed and I had bad xml in my resourcecache in the obj folder.

obj\Debug\resourcecache\DA97546C26E54413F6BB75B0531999D2 \res\anim\abc_fade_in.xml(2): error APT0000: Error parsing XML: syntax error

Specifically the files were Android source files. E.g. res/anim/abc_fade_in.xml or res/anim/abc_slide_out_top.xml.

How does this work? Well, when you add a nuget package either explicit (as with Xamarin.Forms) or implicit (as its dependencies) they are downloaded to your packages folder in your solution. When you build your solution, these are unpacked and cached in /Users/<username>/AppData/Local/Xamarin folder. One subfolder per reference and version. Like so:


This is were the bad xml came from. As it happended, Xamarin managed to download the full structure of the source files but failed (silently mind you) to download the content of some of them.

This was the content of one of the files (values-land.xml)


Ah, finally – the error messages really made sense now.

Since these folders only works as a cache, the solution was easy. Delete them.

I deleted the folder at component-level, i.e. AppData\Local\Xamarin\Android.Support.v7.AppCompat. When I did a new build in Visual Studio it downloaded a fresh copy and my build worked.

I of course had to do a clean solution first to get rid of the bad xml in obj\resourcecache.

The pitfalls of LINQ deferred execution

Let’s face it, we all love the simplicity of Linq. The fluent syntax, the easy to read – almost sql-like – syntax. However, there are som pitfalls that I’ve seen colleagues fall into unknowingly. One of them is what is called  the deferred execution.

By design, you don’t execute a Linq command, you only specify it. The execution is not performed until the result is required. Hence deferred.


Take a look at the following code

Albeit a bit contrieved it is not an unusual pattern. I have a large list that i narrow down to a subset that I would like to work on (zip codes, gender) and then I examine this subset by looping through it.

On my machine this took 15000 ms (I’ve removed the Stopwatch stuff for clarity). This is not reasonable even though we have 1,000,000 records.


The reason is that listSmall is not a list (yet)! It is just a defined query. So, every time we execute

listSmall.Where(o => o == 100100 + i).Single()

we are, in fact, executing

list.Where(i => i > 100000 && i < 150000).Where(o => o == 100100 + i).Single()

So, instead of going through 50,000 records a 1000 times, we are searching 1,000,000 records! Not what we intended indeed. The way to solve this is to force Linq to execute the initial filter. The easiest way to do this is to simply append ToList() at the end. Like so:

var listSmall = list.Where(i => i > 100000 && i < 150000).ToList();

Now, the code runs in 400 ms. That’s what I call improvement.


Another scenario that has it cause in the same Linq feature. Inspect the following code

Here we have a recordset that contains a lot of users and I want to select and group all users from specific years. I loop through the set and select the users. I then store the result in an array. Imagine my surprise when I later loop through my yearbook and see that all users are from the same year. What happended?

Well, since I didn’t, actually, retreive the users in the first loop but only specified the query, when I finally did execute the query the loop is done and i == 0. Through closure, i is visible to my query snippet and is used to select users but – by then – it is 10.


The solution is once again to force execution by appending ToList() to the where statement at row 15.

Happy LINQing.

Debugging your iOS application with Fiddler

Many times I find myself in a situation where I need to monitor the http traffic from my apps. Normally – no problems – just go to Network settings -> Ethernet -> Advanced -> Proxy -> Check the http proxy and enter the address and port number of your fiddler instance.

Oh, and of course, your fiddler instance has to allow remote clients like so:


However, when you want to connect through https, things are getting problematic. At least in the simulator. For the real device? No problemo. Just set the same setting for the proxy as above, and then browse (in Safari) to ipv4.fiddler:8888. This will open a web page generated from fiddler with a link to the certificate needed to allow Fiddler to act as man in the middle. Tell iOS to trust and install the certificate and you are good to go.

So. Now. The simulator has no network settings since it is using your Mac as a gateway. This means that when you’ve set your Mac to use Fiddler as a proxy, your simulator will too.

But when your code use the network stack, let’s say through NSURL, an exception will occur. The error will be something like

ERROR Error Domain=NSURLErrorDomain Code=-1202 “The certificate for this server is invalid. You might be connecting to a server that is pretending to be “xxx.azure-mobile.net” which could put your confidential information at risk.” UserInfo=0x7526530 {NSLocalizedDescription=The certificate for this server is invalid. You might be connecting to a server that is pretending to be “xxx.azure-mobile.net” which could put your confidential information at risk., com.Microsoft.WindowsAzureMobileServices.ErrorRequestKey=<NSMutableURLRequest…

A nice, man-in-the-middle warning. DON’T GO THERE! However, since we actually want this scenario let’s make the simulator trust the certificate. The information about this is stored in a sqlite database in your ~/Library.

So, head over to ~/Library/Application Support/iPhone Simulator/<version>/Library/Keychains.

The you’ll find the TrustStore.sqlite3 database. If you’ve installed SQLiteManager, just doubleclick on the file. You’ll see a table (the only one) called tsettings. Before iOS 5 you just needed the SHA1 (of your certificate) as the lookup key and you were good to go. Not so anymore. Lucky for us there are plenty of Python scripts that will do this for us. Head over to Github and download iosCertTrustManager.py. Put it in /usr/local/bin.

Done? Good. Before we can use the script we have to get our hands on the actual certificate. Open, on your Mac (make sure it’s still in proxy mode), http://ipv4.fiddler:8888  and click on the certificate link and install it on your Mac. Now, open your KeyChain and find the certificate, right-click and export it as a PEM-file. Remember where you saved it.

Open a shell.


“chmod +x /usr/local/bin/iosCertTrustManager.py”

to allow execution. Now simple execute

iosCertTrustManager.py -a <path-to-the-certificate>/DO_NOT_TRUST_FiddlerRoot.pem”

assuming you kept the default name of the certificate. It will now start to ask questions like “.. import to v5.0?, v6.0?” and so on. Just answer yes to all of them.


Avoid memory leaks in .NET

This is something that often bites new developers. “There can be no memory leaks in a garbage collected runtime”. Well, perhaps not in theory, but in real life under the wrong circumstances there will.

Ok, not memory leaks in the terms original meaning, unreferenced memory, but memory you thought you got rid of but it hangs around never the less.

In my experience it mostly happens when we use either Events or Timers. The scenario for events is likely a view-driven application where we pop views in and out of existence. During the lifetime of the view it likely have to respond to events from the host window. Events like “the user clicked the save-button” or similar.

So, during initialization of the view it hooks up to the ev_Save-event in the host. Later, when the user switch view, you drop the reference to the old view and replace it with another one. Gone. Right?

No, the view you just disposed clings on for dear life to the event, and is not eligable for garbage collection.

I have a class representing the view called Worker. I simulate adding 10000 views and then print out the memory consumption.

Note that I’m not saving any references to it. Much like just adding it to the current view. I’m passing in a reference to the hosting window which the client uses to hook up all of the events for interacting with the user.

The constructor of the client “view” just hooks up the fake “save”-event. The heavy byte array is just to make the leak more visible in Task Manager.

When I press the button invoking the “save”-event I can see that my array of listeners contains all the 10000 objects.

Remember I didn’t keep any references to the clients. But rather, the client kept a reference to the host.

leakyLook at this amazing piece of software 🙂

Anyway, to my surprice I hit 10000 save-events instead of the one on the screen.

The easiest way to mitigate this is to make sure the client unsubscribes to all events before you loose it. The perhaps cleanest way to do this is to implement the IDisposable interface and then, during the view-switching, invoke the Dispose()-method.

I simulate this in my handler for the “Dispose”-button

A comment on calling GC.GetTotalMemory(true). When you pass true, the runtime will perform a full GC before returning the memory numbers.

Also, you will not get all that memory back. I.e. it will not drop to its original size. The application will keep the allocation, but regard it as usable. So when you click on allocate again after pressing Dispose, you won’t get an OutOfMemory exception. This is just the way .NET works

This scenario is, as I mentioned above, very common in Silverlight- and WinForm applications. Perhaps you are using MEF or Jounce or any other helper library that makes the tedious view plumbing go away. But it might also make you think that all this is automagically taken care of.

It is not.

Sample project here