CoverOn Sunday, I went to GOOS Gaggle, a micro-conference on the development ethos described in  "Growing Object-Oriented Software Guided by Tests", the new book written by XP stalwarts, Steve Freeman and Nat Pryce.

After the main presentations, we moved into Open Space format. I joined a conversation with John Daniels and Willem van den Ende about "Why Start with End-to-End Tests?". Although we agree whole-heartedly with this, John was interested to explore whether this approach is always a good idea? You can read John's write-up of our conversation on his blog.

John starts by writing this up on the board.


When you start solving a problem from the outside, you ensure that inner workings connect to the real world setting. You start to grapple with all the interfaces to the system from user interface to the back end activities of logging and persistence. An excellent way to flush out any issues that might catch us out and require rework later on.

We wonder if the reason working outside-in and creating end-to-end tests is the simplest way to ensure we tackle risks early. John suggests that the biggest risk on some projects could be in the inner logic, for instance if the project was based on running complex calculations. Maybe there are situations where an outside-in approach may not be the best one to take?

Then I rack my brain trying to remember past projects where we didn't start end-to-end. What were the barriers that stopped us doing this?

The first example I remember was back in 1994 when I was working on a broadband switch demonstrator. My company was providing the call-control component but we were working in a consortium where other companies were providing other components that we would interface to, such as a set-top box, etc. Message protocols were not agreed and the hardware was work-in-progress but we had a hard deadline to demonstrate the kit at an industry expo. We did the only thing we could to make headway. We made-up a reasonable message protocol and then worked against software stubs which piped in messages in our imagined protocol. When the real interfaces were revealed, we mapped them into our own internal protocol, on the way in and out. This worked really well for us. We made the trade show deadline. Another example is more recent. A team I am coaching are building on some content-management infrastructure being developed by another department. It's not ready and they've been trying to work out whether to: wait, work on other features, or build their own solution using existing infrastructure.

Realistically, sometimes you need to make a start without having full end-to-end picture.


Our worry is that sometimes teams may prefer the "path of least resistance" because it's easy or they're naive about integration.


However, we ought not to forget that sometimes the biggest risk is organizational politics. It can be important to demonstrate progress to get buy-in from key stakeholders. Scrum can be perfect for mitigating such risks. We work on tangible product backlog items that we can demonstrate every few weeks. This builds trust in the team's ability to deliver on their commitments.

Willem adds that it can be hard for a team to justify "technical" product backlog items that mitigate risk over juicy features with obvious business-value. The team can attempt to make the value of such technical items more obvious by linking them to the money lost in downtime when a site crashes or security is breached.

Another common approach is to pair a Business Product Owner with a Technical Product Owner for projects where there are lots of infrastructure considerations. John pointed out that there's likely to be a tension between long-term technology decisions and short-term project goals. This is where it can help to have a project manager facilitate decision making. Thus, you need a three-way balance (as in this sketch) rather than (as we see too often) the Scrum team kowtowing to Product Owner without speaking up on technical risks.

Perhaps one of the main values of the GOOS approach and working from outside-in guided by tests is that we are able to flush issues out early rather than attempting to anticipate them. Thus we avoid awkward conversations with a Product Owner about potential risks because the issues stare us in the face having driven them out with end-to-end tests.