Designing for Testability

This is a segment that I wrote for a book used internally and with Microsoft partners.

Building a car may seem like a complicated process (because it is), but imagine if the design of the car changed on a daily basis. Also imagine if the tools and processes changed daily. With few things being constant, creating a quality automobile would become increasingly difficult. Welcome to the world of software engineering. The factory is your favorite editor, the cars are your code, and the customer is everyone.

The reality is that all developers test their code. How many times have you made a change, compiled the code, waited for the application to run, and then navigated through the application to execute the code you just wrote? The problem is that efficiency goes down dramatically the longer you have to wait to see a result from the changes you make. Looking back at the car example, would you rather buy a car whose quality was checked in every step during construction, or would it be acceptable if the testing was done only once the car was assembled? Considering the higher potential for significant re-work and the associated schedule impact when testing is deferred to the end, which approach do you think will prove faster?

Avoiding bugs is much more enjoyable than having to fix bugs. Features such as type systems exist to join the “result” of the code with the creation of the code. Defining a variable to be a particular type is actually a specification or test definition that runs at compile time against all usages of that variable. Languages like TypeScript allow us to use the full power of a dynamic language like JavaScript, with the safety of a type system.

Since software development is highly dynamic, there is no single way to build applications, but we can increase code and app quality by following proven principles. For example, the SOLID principles published by Robert C. Martin provide some fundamental tenants.

SOLID is actually an acronym of 5 other acronyms, defined below. With good design principles comes testability. Testing is a word that typically strikes fear into the hearts of developers. Like many fears, understanding removes the fear. In fact, a good unit test should be simple, useful, and actually saves development time. Using that definition, it’s not possible to have a unit test that will “cost” you time.

Instead they provide you with immediate value.

SRP The Single Responsibility Principle A class should have one, and only one, reason to change.
OCP The Open Closed Principle You should be able to extend a class’s behavior, without modifying it.
LSP The Liskov Substitution Principle Derived classes must be substitutable for their base classes.
ISP The Interface Segregation Principle Make fine grained interfaces that are client specific.
DIP The Dependency Inversion Principle A class should have one, and only one, reason to change.
SRP The Single Responsibility Principle Depend on abstractions, not on concretions.

(source: Agile Principles, Patterns, and Practices in C# by Robert C. Martin)

The figure below illustrates this difference. Code not designed for testability will be, well, largely untestable. This is what typically deters developers from making testing part of their development process. As we learn how to craft our code into well designed components, the amount of code that is easily tested will be the majority. There will be some additional code that has a questionable return on testing investment, and code that will never make sense to test. The Y-Axis is the degree of testability, or the ease of which a particular piece of logic can be tested. The X-Axis is defined as “benefit,” which is comprised of how often the code will be reused, the importance of the code, the complexity of the code, and the risk level associated with the code not working as expected.


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Sending Real-Time Sensor Data to Clients Using SignalR

You don't have to go very far into the past to find yourself in a time where pushing data from a server to a client was a huge pain. Sure, you could use tricks like polling or long-polling, but it was difficult and error prone. Fortunately, we have technologies today that make it drop dead simple without complexity or bad performance.

If you're using a technology like Node.js, then something like or Faye is for you. They're not the focus of this post, but they are both extremely easy to use.

Instead, I'll be focusing on an ASP.NET MVC application that will send data in near real-time to a web client.


SignalR is based on the concept of hubs. You create hubs in your .NET application (ASP.NET/MVC/etc). Here is what a simple hub can look like:

public class ChatHub : Hub
    public void Send(string name, string message)
        Clients.All.broadcastMessage(name, message);

If you haven't used SignalR, Be sure to familiarize yourself with the above example before moving on. The server calls the Send method, and that method calls broadcastMessage on all of the connected clients.

SignalR is awesome for a few reasons:

  • It makes our life easy by hiding the complex process of determining how to connect to a server.
  • SignalR is also extremely fast. It's hard to find benchmarks, but I've read reports of getting 10,000+ calls/sec with a single server.
  • It is possible to scale out to multiple servers.

The Scenario

In my manufacturing projects, I wanted an easy way for web clients to subscribe to real-time data streams.

Real-Time Data Feeds

On the left is a list of streams that the user can subscribe to, and the chart on the right plots those values as they arrive from the server.

The Server Implementation

The easiest way to wire up SignalR for our scenario is to use the Microsoft ASP.NET SignalR OWIN Nuget Package. OWIN gives us an easy way to inject functionality into our server. To enable OWIN, we'll also need to pull in the Microsoft.Owin.Host.SystemWeb Nuget Package.

Once those packages are installed, SignalR can be wired up simply by adding a file with the following contents:

using Microsoft.Owin;
using Owin;

[assembly: OwinStartup(typeof(MyNamespace.Startup))]

namespace MyNamespace
    public class Startup
        public void Configuration(IAppBuilder app)

That's how easy it is.

Let's talk hubs. A hub is just a regular class that inherits from Hub. Just keep in mind that hubs are transient, meaning that anything you store in a member property will be lost in the next call. That's actually a good thing since we may be spanning multiple servers. Storing any state should happen outside of the hub.

Now, let's create our first Hub:

using Microsoft.AspNet.SignalR;
using Microsoft.AspNet.SignalR.Hubs;

namespace Manufacturing.Api.Hubs
    public class DatasourceRecord : Hub

It doesn't do anything yet, but it gives us a place to put our methods.

To allow clients to subscribe to the streams they're interested in, I'm going to use a feature in SignalR called Groups. Groups give us a way to fan out data to clients that belong to that group. Remember how I said that hubs can't store state? Groups do store the mapping between clients and group names.

Let's provide some methods for the client to register for streams they're interested in:

(Note: I call them Datasources)

    public const string GroupLabelPrefix = "Datasource_";

    public void Register(int datasourceId)
        Groups.Add(Context.ConnectionId, GroupLabelPrefix + datasourceId);

    public void Unregister(int datasourceId)
        Groups.Remove(Context.ConnectionId, GroupLabelPrefix + datasourceId);

Context is an inherited member that allows us to look up the unique ID of the client making the request. By adding and removing clients in the groups, they're explicitly subscribing to what they're interested in. Security could easily be layered into these methods as needed.

Here is the method call to get data to the subscribed clients:

public static void NewDataRecord(DataRecord record)
    var context = GlobalHost.ConnectionManager.GetHubContext<DatasourceRecord>();

    var groupName = GroupLabelPrefix + record.DatasourceId;
    var group = context.Clients.Group(groupName);
    if (group != null)

Notice that this method is static, which was intentional. This allows us to easily call into the hub from code elsewhere. In my case, I'm receiving data through Azure Event Hubs.

The Client Implementation

For the web client, we need to pull in the SignalR client libraries. We can get these with the Microsoft.AspNet.SignalR.JS Nuget package.

Now add a reference to the client library in your HTML. We also need to reference a special script called signalr/hubs. This second reference is a dynamically generated client library based on the server methods that we'll define later.

<script src="Scripts/jquery.signalR-2.2.0.min.js"></script>
<script src="signalr/hubs"></script>

Now, we can reference our hub and handle server events:

dataHub = $.connection.DatasourceRecord;

dataHub.client.newRecord = function (record) {
    console.log('Record from server: ' + msg);

SignalR is handling all of the serialization/deserialization of the record, so we actually get back a JavaScript object, not a string.

It's important to subscribe to at least 1 event before starting SignalR so that the hub gets started. Now, let's initiate the connection:

$.connection.hub.start().done(function () {
    console.log('Connected to SignalR hub')
}).fail(function (err) {
    console.log('Failed to connect to SignalR hub ' + err);

And when we want to call the server to subscribe to a stream:



CORS is a horrible, horrible pain that masquerades as security. If you want your SignalR hub to be hosted on a server that is different than the server that hosts your front-end, you'll need to include the Microsoft.Owin.Cors Nuget package and use the following code in your OWIN startup:

app.Map("/signalr", map =>
    var hubConfiguration = new HubConfiguration();

More Information

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How We Produce the MS Dev Show Podcast

Update 2016-01-04: I have some hardware updates in a newer post

We've gotten a lot of questions about how we get great sound on the MS Dev Show. From the start, Carl and I knew that great sound wouldn't make us successful, but bad sound could definitely hurt us.

A lot of podcasts have just... ended. It seems to happen somewhere between episode 20 and 100. I knew how important it was to make the podcast take the absolute minimum time commitment.

Today, I'm sharing our entire process.

Many podcasts won't talk about this. I'm not sure if it's too much inside baseball, or if they think they are trade secrets. Well, I'm all about sharing.

From a high-level, we find guests, prepare, record, edit, and publish.


Guests are a big part of our show. We've always wanted to have interesting guests. We occasionally have some names you've heard of, but we also love to have guests that haven't been on a podcast before.

I believe that everyone has a story, and we want to hear it.

Since guests have to take time out of their important schedule for us, our goal is to make it as easy as possible, with a minimal time commitment. Once a guest accepts and we work out a time slot, we have a template invite we send them. Templates are absolutely key to our communications, and allow us to be clear and concise. As we improve our process, we evolve our templates.

Email Template Example

Around 24 hours before the episode is scheduled to record, we send another email template that contains a rough idea of the questions Carl and I want to ask, and everything the guest needs to know to get set up. More on that later.


OneNote is what powers the MS Dev Show. All of our processes, templates, and episode details are in a OneNote notebook that Carl and I share.

OneNote Screenshot

As Carl and I come across stories we think would be worth discussing, we put links into a OneNote page for the associated episode.

We also use OneNote while we're recording, back to that in just a bit.


You might think this is the most important part, and you'd be partially right. For our mics, we copied TWiT, and use the Heil PR-40. At ~$330, it's pricey relative to other mics, but cheap compared to the computer you're plugging it into.

Heil PR-40

Lesson time. The Heil is a dynamic microphone. Some people use condenser mics, but condenser mics do a horrible job cutting out background sound. Dynamic mics do a good job of only picking up the sound right in front of them. This is key for Carl and I since we're recording from our home offices and have kids and pets.

If you want to hear the difference between a USB headset, and the mics Carl and I use, check out this track that I recorded shortly after getting the Heil:

Our mics are connected to the Alesis IO2 Express. This is what converts the signal from our mics to USB to connect to our computers.


Using an insert cable, we route the mic sound through the Behringer MDX1600 compressor/gate/limiter. This primary serves to "gate" our audio, or essentially turn it off when we're not speaking. This is our first line of defense against barking dogs, screaming kids, and loud keyboards. I now believe this equipment is optional thanks to improved software processing that I'll describe later.

Behringer Compressor/Gate/Limiter


Around 24 hours before we record, we send the guest an email reminder with additional details.

Pre-Show Email

We use Skype to talk to our guests. One lesson learned with Skype is that it auto adjusts your microphone volume by default. It has a tendency to boost the gain if you don't talk for a while. When you start talking again, it blows out the audio, and sounds terrible. I manually adjust this setting by speaking at a normal level, allow it to auto-adjust, and then uncheck the box.

Skype Auto-Adjust Mic

Carl and I both use Callburner to record all sides of the conversation. Since we both have complete copies of the call, we can be fairly confident that even if we have a technical failure, we'll still be able to fall back to a second copy.


We always record our tracks in raw WAV format:

Callburner Settings

Additionally, we ask our guests to record their own microphone input. We include simple instructions to make it as painless as possible. When everything goes according to plan, we have a separate track for every person on the call. One track for me, one track for Carl, and one track for the guest.

As we go through the episode, we use OneNote as a guide. We use it to make sure we don't forget any big, important questions, and we use it to mark off questions that were already asked. Since OneNote updates on both sides in near real-time, it allows us to run the show as we go, without stopping or IM'ing.


Short version: trim, Auphonic processing, truncate silence, finishing touches.

First, I use Audacity to trim the tracks. Audacity is free software that works amazingly well. There is always some pre-show and post-show chat, so I cut them down to the meat, and make them all the same length.

Next is noise reduction. This is an area that can eat up a lot of time if you let it. In the early episodes, I did minimal manual edits. As I started to desire higher quality, I found myself spending more and more time on editing. We're not talking about major edits, it was more about removing breaths, clicks, etc. I was getting desperate to cut this down. I was willing to try anything. I even tried Adobe Audition, but it is obvious that it wasn't really designed to edit a podcast. Don't get me wrong, it's fully capable, it's just not optimized for a podcast workflow.

Then, a miracle. I found a website called Auphonic. It's unbelievable at processing audio. It has amazing noise reduction, which is key for guests since they don't have gates. It also intelligently focuses on the track of the person that is speaking, and attenuates the other voices. This is amazingly effective. Other than our gate, this is the only audio processing we do. This software is good enough that you could skip the compressor/gate/limiter completely. It works fine if you have 1 track, but even better if you have separate tracks for each speaker. All of the settings we use for the show have been saved as a preset, so it takes less than 60 seconds to submit a processing job.

Auphonic Output

After Auphonic works its magic, I bring it back into Audacity. Then, I use a feature called truncate silence (under the "Effect" Menu). This is one of our best kept secrets. It takes out pauses in the audio that are longer than a certain duration, and shortens them up. The end result is that even if someone takes a moment to answer a question, it will sound like they answered without pausing. In a typical hour long episode, this takes out around 4 full minutes.

Truncate Silence Menu Item

Adding the Intro/Outro

I record the intro text directly into audacity. "Welcome to the MS Dev Show, episode number....". I place this track below the intro music track. Then, I use the "Auto Duck" option under the "Effect" menu. This automatically turns down the volume while I'm talking. If I had a long pause in the intro voice, the theme music would actully come back up and fill it in. Lastly, I use the Envelope Tool to make the intro sound fade in. I started doing this since the riff at the start of the intro can be a bit glaring.

Ducking the Audio

The outro is pre-recorded for convenience, and I just put it at the end.


The easiest way to publish your podcast is to use Libsyn. It's fairly inexpensive, and you pay monthly for new episodes. The great part is that you don't pay for old episodes. They handle everything for you from hosting the files to providing the feeds that you can submit to aggregators like iTunes and Stitcher. Make sure you check on those services to ensure the feed is set up the way you want.

Carl handles the shownotes, and these are created by exporting them from OneNote to an mht document, and then using PanDoc to convert to markdown to publish to our website.

Our website is completely open source. You can see all of the code in GitHub. You can even fork the site, create your own, or issue pull requests. The website itself is hosted in Azure, and automatically redeploys when we check in a change to GitHub.

Feel free to watch the commit log. You might even get a sneak peek at an episode before it's published!

GitHub Changelog


I made a quick video showing the editing process:


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Jason Young I'm Jason Young, software engineer. This blog contains my opinions, of which my employer - Microsoft - may not share.

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