Automated testing: a practical guide

It comes up on almost every project, usually later than it should. This guide covers what automated testing actually involves, where it usually goes wrong, and how to tell whether yours is in reasonable shape.

Most development decisions are really maintenance decisions wearing a different hat. Nothing below assumes a large team or a large budget — most of it is a decision somebody has to make and then write down.

The reason this keeps coming up

Tests are how you change things without fear. In practice this is a scheduling problem more than a technical one. If it only works because one person remembers to do something, it does not work yet.

For most businesses the question is not whether this matters but how much of it is worth doing right now. That depends on what you are trying to achieve in the next few months, not on best practice in the abstract. The cost of getting this wrong is rarely visible on the day it happens.

The practical version

Cover the paths that lose money if they break. The cost of getting this wrong is rarely visible on the day it happens. The version that survives contact with a real deadline is the simple one.

The question is rarely whether something can be built, but what it costs to keep running afterwards. The version that works in practice is usually less elaborate than the version described in the guides.

A slow test suite is a suite nobody runs. The teams that handle this well are rarely the ones with the biggest budgets. It rarely shows up as a line item, which is exactly why it slips.

A working checklist

If you want a quick read on where you stand, work through this. Anything you cannot answer confidently is where to start.

• Tests are how you change things without fear
• Cover the paths that lose money if they break
• A slow test suite is a suite nobody runs
• Someone is named as the owner, not just assumed to be
• There is a date in the calendar to review it again
• The decision and the reasoning behind it are written down somewhere findable
• You could explain the current setup to a new hire in five minutes

Common failure modes

The most common failure is not doing this badly. It is doing it once, during a launch, and never revisiting it. Circumstances move, the setup does not, and the gap widens quietly until something breaks or somebody notices the numbers.

• It was configured during a launch and has not been touched since
• Different people in the business believe different things are true about it
• There is no way to tell whether the last change helped or hurt
• The only person who understands it has left, or is about to

Code gets read far more often than it gets written, and usually by someone with less context than the author had. The cost of getting this wrong is rarely visible on the day it happens.

How we approach it

On our projects this gets handled during the build rather than added afterwards, because retrofitting it costs several times more than including it. We write down what was decided and why, so the next person to touch it is not guessing.

If you are working with someone else, the questions worth asking are simple: who owns this, how will we know it is working, and what happens when it needs to change?

Making it stick

Pick the single item from the checklist above that would cause the most trouble if it turned out to be wrong. Fix that one, confirm it worked, then move on. None of this needs a rewrite. Most of it is a morning's work once someone decides to do it.