Test-Driven Development is not about testing

An early morning last month (October 2016) a mix of software developers from several teams of Bonnier Broadcasting gathered in the cosy offices of Agical in Gamla Stan to spend a full day listening to the wise words of Mr. J. B. Rainsberger on the topic of TDD — Test-Driven Development.

Here follows an attempt to distil some of my reflections and take-aways from the event in the form of a combined summary and short intro to the topic.

What is a test; what is TDD?

As developers we are human, and as humans, we err. Writing tests is a way for us to eliminate, or at least reduce, errors by ensuring that what we build functions in the way we expect. If we write code that can add two numbers, we might write a test that asserts that given one plus two, we get three.

TDD takes the idea of testing a step further by in essence letting the test define correct behaviour, as opposed to verifying correct behaviour after the fact. Writing tests early on turns out to have positive effects not only on the correctness of our code, but also its design, with reduced coupling and better separation of concerns — perhaps this is the greatest benefit of TDD.


Many things were covered during the event and it would have been odd if everyone went home with the exact same insights. Here are just a couple of take-aways that struck me as having particular value.


Design is hard. Done well it brings many benefits and can be intellectually rewarding. Done wrong it can be the cause of high costs both financially and in the form of lowered productivity and motivation.

TDD is not a silver bullet that magically solves all design problems, and I will not claim that TDD is essential to designing things well, but it is a valuable tool that if used right allows us to find design mistakes early so that they may be corrected, before they become expensive. Rainsberger relates to the concept of risk exposure.

E = ∑([pm * cm, …])

Exposure is the sum of the probability of each possible mistake multiplied by the cost incurred should it happen.

To reduce exposure we may choose to reduce the probability of a mistake — in essence figuring out the potential mistake before it happens. If it is true that design is hard, then predicting future mistakes is not a trivial task.

Alternatively, we could assume that mistakes will be made and instead try to reduce their cost.

Code that is easy to test tends to be better designed, since — and one could almost get away with giving the inverse as the reason — well-designed code tends to be easier to test. It is like a virtuous circle, and also a concept within TDD; write a test, implement, test, refactor (improve the design), loop. This way TDD helps keep a clean design. If we only take care to watch for the tell-tales indicated by how straightforward and clear the tests are, it is easier to, at an early stage, spot potential flaws in our design.


When designing we make certain assumptions. That code that adds two numbers might assume that its arguments are numbers. In a statically typed language this particular case is of course automatically enforced. In a dynamically typed language, it has to be assumed or checked. This is a precondition for the code to work correctly and essentially becomes part of its contract, whether explicitly documented or not.

Another example is the Read method as defined by the interface io.Reader of the Go standard library. Read is used to read bytes from a data source by copying it into a given buffer p. Its contract states “if some data is available but not len(p) bytes, Read conventionally returns what is available instead of waiting for more”. It is the responsibility of the caller to be aware of this behaviour.

Assumptions always exist about how the code we write will be used, and about how code we use behaves. A clear contract not only defines what can and cannot be expected, but it helps define to what extent the code should be tested. While some things are difficult to capture in a test (such as unexpected behaviour), writing tests can be a nice way to explicitly demonstrate what kind of usage we expect and support.

Unit tests vs. integration tests

A unit test serves to test a small part of a system in isolation.

A unit test:

  • …is isolated
  • …is simple
  • …is small
  • …runs fast
  • …is clear on what is being tested
  • …makes it easy to pinpoint the cause of specific failure
  • …drives design

An integration test serves to test how multiple layers of a system work together as a whole.

An integration test:

  • …tests many parts of the system as a whole
  • …might make calls to things outside of our control
  • …can fail in many different ways
  • …is slow

Side note: Rainsberger would correct the term “integration test” replacing it with “integraTED test”, defining it such that an integraTION test tests isolated points of contact between two parts, whereas an integraTED test is, quote, “any test whose result (pass or fail) depends on the correctness of the implementation of more than one piece of non-trivial behaviour“. While these definitions are clear in themselves, the use of two similar-sounding terms to mean different things tends to cause confusion (cf. authentication vs. authorization — both conveniently abbreviated ‘auth’), so I choose to simply walk around the definition swamp by using the term “integration test” to mean what Rainsberger calls “integrated test”, and for the time being avoid this other definition of “integration test”. How to name things: one of the hard problems in programming.

Rainsberger metaphorically compares the two methods of testing saying that the former is like painting a wall with a brush, while the latter is more like trying to cover all of it by throwing buckets of paint at it.

He describes the latter kind of tests as a scam and drew for us a vicious circle, illustrating that the more we start to rely on these tests, the more we lose the ability to iteratively improve our design, which in turn negatively affects the ability to write isolated unit tests, in turn resulting in even more end-to-end tests being added.

Perhaps one can extend the paint metaphor by saying that the more buckets of paint we throw at the wall, the harder it gets to move closer to it without getting our feet covered in paint.

Above being said, it should be pointed out that acceptance tests for the purpose of verifying behaviour from the end user’s point of view are perfectly fine, as long as they are not used as a substitute for tests which are usable in driving the design.


Even for someone already at least somewhat familiar with the idea of TDD I found it refreshing to during this event be able to reiterate on some of the concepts.

For the past two-or-so weeks we tried forcing ourselves to use TDD at one of our mob stations. In the context of mob programming it turned out to be quite useful in defining something of a road map of what to do next, and also as a means to keep focus on a particular task.

The most important insight that I gained from this day deserves its own line:

TDD is not about writing tests, it is about writing better code

Lastly, some things noteworthy.

  • – Prepare for design change from any direction.
  • – Not prepared for any particular change, but prepared for change
  • – Test integrations with external parties in isolation.
  • – Abstract external parties using interfaces, exposing only what is needed.
  • – Avoid mocking types that you don’t own.
  • – Do not pass nil to things intentionally.
  • – Complex mocks can be an indication of bad design.
  • – Make the documentation clear, entertaining, and small, with code examples.
  • – 100% test coverage does not necessarily mean that all logic is being tested.
  • – A worker should never talk directly to the client in multi-threaded code.
  • – Test the worker in isolation; it should not know whether or not it is being called asynchronously.
  • – Avoid large anonymous functions, because they are hard to test in isolation.

I shall also add that the above are my own interpretations, and as such do not necessarily correspond exactly to the ideas presented during the event.

Thank you for reading.

A platform for our platform

In June this year (2016), a new team was formed within Bonnier Broadcasting with a mission to build a realtime data platform. The purpose being to address a set of high priority data needs we have identified, but also to support the growing data driven culture we see in both C More and TV4. A realtime data platform has of course no formal definition, and it can mean slightly different things to different people. To us, it means an accessible data warehouse where all our data sources are consolidated and integrated. These data sources range from relatively static sources, such as user or video databases, to event streams from apps and services, ingested in realtime. From all these sources we need to create data models, analysis, and visualizations that help the rest of the organization do a better job.

So, when starting out on this journey, one of the first questions to arise was, where should we build this platform? What platform should we choose as the foundation for our platform? This post recounts the reasoning behind our choice, and our experiences with the result so far.


We went with Google Cloud Platform for our data platform and we are mostly happy with it.

A cloud platform

For the majority of our system components (infrastructure services, databases, video platform) we have already made the move to the cloud. Several years ago we started using AWS and Heroku (and we are still migrating legacy services). At the time there were not many options, and we are still happy with AWS for our core needs.

This year, however, when discussing our future data platform, the cloud landscape has evolved substantially from when we picked AWS, and we saw an opportunity to take a step back and evaluate our options. And there are a host of options these days, at various abstractions levels, and with various levels of managed offerings.

Apart from pure functional requirements, of which none is particularly unique, we have a few non-functional constraints that effectively narrow us down a bit.

First, we want as much control as possible. We want to avoid, or at least minimize, vendor lock-in and dependencies to third-party products and solutions. This rules out a number of packaged solutions, such as Cloudera, Databricks, MapR, and others.

Second, we are a small team with an ambitous task. We want to minimize, as much as possible, the cost of operation and maintenance that comes with doing too much ourselves. The most obvious path from there would perhaps be to go in the Apache direction, where Hadoop, Spark, and an abundance of other tools, await the willing, and set them them up on our AWS account. Much, if not all, of what we want to achieve has already been done with these tools, and many well-known companies have contributed to the toolbox over the years.

However, a third constraint is that we have picked Go to be our language of choice. This is a conscious choice, made from a number of reasons (which I would be happy to share in a separate post). As a consequence, we have invalidated (or at least made awkward to use) from our list of options the majority of open source data processing tools and frameworks, which are available to your everyday Java, or Scala based shop.


Google Cloud Platform (GCP) has been moving forward at tremendous speed during the last year(s) to catch up with AWS, trying to establish itself as a serious contender in the cloud market. And with Spotify announcing early that they are migrating their data processing platform to GCP, the risk associated with making the same move was substantially lowered.

As it turns out, what Google Cloud wants to be matches our needs and constraints to a very large extent. Most, if not all, of the infrastruture we need is there. The following four components are what we use the most today.

  • BigQuery is the managed data warehouse we needed but did not find in Redshift.
  • Container Engine (GKE) is the managed Kubernetes platform we don’t have to waste our own time on setting up and maintaining.
  • Dataflow is the managed data processing service that automatically runs and scales our stream and batch jobs, that we write with Apache Beam/Dataflow.
  • PubSub is the managed message bus that we use to pass data between the services above.

A key word here is managed, and it translates to a huge amount of time and effort that our small team does not have to spend on stuff (e.g. setting up, configure, monitor) that is not pushing our data platform forward.

Many people I talk to seem to look at GCP as simply a Google version (albeit less mature) of AWS or Azure, that aside from subjective bias and pricing, they have more or less the same offering. Having started out with AWS for our platform, we have found this assumption to be false, at least when it comes to our use case. The managed aspect of the GCP services is a differentiator.

What about Go?

The third constraint I mentioned above was the Go language. These days, the JVM is the ruler of data engineering, and to a large extent data science as well. As a consequence, we are not completely free from the JVM dependency, as much as we want it. What’s holding us back is Beam/Dataflow, where the stream processing SDK is still only available in Java. The Python SDK is moving along, however, and there are rumors that a Go SDK is in the works somewhere inside Google. Hopefully we can contribute to that once it is released to the community.

However, since all Google Cloud API’s have official Go client libraries (of which most are hand crafted and idiomatic, and not generated from spec), we can do most of our plumbing and infrastructure in the language we feel gives us most speed and quality.

The flip side

When I earlier wrote about what Google Cloud wants to be, I was hinting at the major downside we have experienced with our choice of cloud platform. Several must-have’s for us in terms of functionality are still in beta, or even alpha, and one or two GA components are still lacking (I’m looking at you, Stackdriver). Each component is moving at a very high speed, and one shouldn’t invest too much effort in trying to work around a current limitation, as it may well be solved two months later.

So, while moving in the right direction at high speed generally is perceived as a good thing, it is also frustrating when you try to build something real on top of it. We wouldn’t want it the opposite way though, and all in all we are happy with the choice we made.

AWS Meetup TV4

24. Augusti anordnas tredje AWS meetup i Stockholm. TV4 sponsar meetupen med lokal, dryck och mat.

Agenda för kvällen:

  1.  Short Host and Sponsor Welcome
  2. Sanoma Nelonen Media Broadcasting infrastructure
  3. MaaS Global and Serverless architecture on AWS
  4. Streaming setup for C More on AWS.
  5. Rovio’s Game Technology Infrastructure in the Cloud Era

Läs mer på http://www.meetup.com/aws-stockholm/events/231792951/

Vi ses från kl 17!


“Vanlisar” sökes till hackathon!

För ett år sedan höll vi ett hackathon på Färgfabriken i Stockholm. Totalt 63 personer i tretton team som arbetade i två dagar på temat “Annons 2.0”. Förutom egna utvecklare och medarbetare från säljavdelningen hade vi team från digitala byråer, konsulter, Hyper Island-studenter och “vanliga ungdomar” som vi hittade via den här bloggen.

Om två veckor kommer vi göra ett nytt hackathon. Det kommer bli annorlunda mot det förra men vi söker deltagare även den här gången, dock inte av samma typ sist. Den här gången söker vi “vanliga människor”. Alltså personer som har någon relation till TV4 men som ska vara där i egenskap av att vara just användare eller tittare. Er insats kommer vara att få tycka till och feedbacka det ni får ta del av.

Upplägget för det här hackathonet bygger på att vi får in användare tidigt i processen. Redan på skiss- och ritstadiet vill vi visa upp hur vi tänker och vad vi vill göra för att få snabb input och relevant återkoppling.

Vi söker därför åtta personer som vill vara med fredag den 26 februari 11-15 på Venue 81 på Drottninggatan 81. Din uppgift blir att agera dig själv och tycka till om de prototyper och skisser du får se. Fattar du vad du ska göra? Vad funkar bra? Vad är otydligt? När skulle du använda den här tjänsten? Hur tänker du att den borde fungera? Ditt tyckande kommer bli en snabb återkoppling till teamen som jobbar på att lösa ett problem. Ingen expertkunskap krävs, bara att du är dig själv.

Vi ser till att du får lunch och energi så du håller dig pigg. I de pauser som uppstår kan du koppla av i fiket och umgås med andra som är där.

Låter det kul? Anmäl dig i så fall här! Och tipsa gärna din svärmor, sambo, frisör,  tandläkare, klasskompis eller soffliggare till kompis om du tycker att de skulle passa.



Vi på B.OTT Android teamet är mycket stolta att presentera vårt första bidrag till Android developer communityn som vi har utvecklat in-house: ett plugin för Android Studio som heter Chronometro.


Open-source är en av anledningarna till Androids framgång. Därför är det extra kul att kunna ge tillbaka till communityn och bidra till fortsatt utveckling av plattformen.

Chronometro används för att mäta laddningstider av metoder och anrop som används i Android applikationer. Den är mycket praktisk för att kunna verifiera icke-funktionella krav.

Så, pröva den gärna och spread the word 🙂