Jonathan Cutrell

Testing Is A Shared Hallucination About Risk


Today in the Guild company chat, someone brought up the Ship of Theseus. The idea is simple: take a given ship. If you replace one part, most reasonable people would say that's still the same ship.

But now, replace every part, one by one. Even better, replace some parts twice.

Is it still the "same ship"?

There isn't a correct answer to this problem. A deconstructionist would say there is no ship. In fact, there's also no wood. Everything is just molecules, and the fact that they happen to be near one another is not scientifically meaningful. The ship, therefore, exists only in your mind. You give it meaning, and therefore the only answer is the one you provide meaning to.

The hallucination trick is that we have a shared meaning of the ship - that any other given person you ask about the ship would agree that indeed, that is the Ship of Theseus. The collective agreement on the meaning makes it something more than a simple hallucination. But, the hallucination breaks down differently under change; "is it still the same ship?" has less uniform adherence than the original concept of the ship.

Testing doesn't exist

This discussion reminded me of another discussion I had recently with a colleague about test strategies.

Most software engineers have as many or more opinions about testing as they do about programming paradigms or cuisine. What shape is your testing strategy? Is it a trophy or a pyramid? Do you do real E2E or do you stub out the services? What is your coverage percentage? Do you test integrations directly? Do you test your private code? Unit tests? Feature tests? Do you automate performance regressions?

Don't get me wrong - these are excellent conversations to have. Often, the most seasoned engineers I know spend more time focusing on writing tests than the code being tested. (This lines up with the reality that code is not the bulk of the work you do - it is just the outcome.)

But if you put two engineers at a bar to resolve to the best testing strategy, there's a close-to-certain chance it will end in a stalemate. Add a third engineer to the mix and you've almost created a perpetual motion machine.

Testing doesn't exist, in the same way that the ship doesn't exist; not because we're replacing the code constantly, but because testing in all of these formats is essentially "more code" (or, in some cases, more button clicking).

What exactly is it that exists? What are the molecules here? Or, what is a more useful layer of abstraction that the 3 engineers at the bar can settle with?

Testing As A Materials Tool

The concept that "testing doesn't exist" shouldn't be incendiary - of course the shared concept does exist. However, what happens if, like Theseus's Ship, we replace some unit tests with some other kind of test... or, more to the point, if we adopt a strict type-safe approach that eliminates the need for some of our unit tests... are we still testing?

Instead of thinking about testing as a primary mode, it is more useful to think about testing as a variety of tooling. Your intent, then, is to think about and manage risk.

How do you decide whether to do a unit test? Risk modeling. How do you decide whether to do manual tests? Risk modeling.

What about feature tests? Trophy? It's all the same. The value of testing is to reduce risk.

"But Testing isn't Just About Risk"

"It's also great documentation," you say, sitting back and sipping your pourover. Yep, sure - the same concept exists here, though! Documentation exists to reduce risk!

Your new engineer onboarding and reading tests to understand what's happening? That learning reduces the risk that they will change something in a dangerous or unproductive way.

So, even for tests that don't directly increase confidence (which carries a loosely inverse correlation to risk), they are still also reducing risk by creating clarity around how your code works to other human beings.

Okay... Enlightenment achieved, everything must be about risk?

No. This is just a useful mental model and thought exercise. I don't actually believe documentation and testing don't exist. This is just a way to determine whether your tests and documentation are actually useful or not.

If your tests are not reducing risk directly or indirectly, what are they doing?

Testing as a Cost Center

Testing in this model can be considered a cost center. If you could achieve equivalent risk reduction without automated or manual testing, why wouldn't you?

Many cost centers are risk reduction mechanisms. Some types of employee benefits (but not all) fit into this category.

For example, unlimited vacation time might be used to reduce risk of employee turnover. There are two sides on this coin; vacation time is also correlated with higher productivity, which also has a positive effect on retention. Calibrating the amount of vacation time, then, becomes an exercise in understanding risk. Too little vacation and you risk burnout and turnover; too much vacation and you theoretically risk too much interruption. The "right" amount is dependent on many factors.

As it turns out, you can nearly 1-1 replace choice words in the above paragraph with testing. Let's try it:

For example, testing might be used to reduce risk of shipping bugs to production. This is two sides of the same coin; testing is also correlated with higher productivity, which also has a positive effect on quality code. Calibrating the amount of testing, then, becomes an exercise in understanding risk. Too little testing and you risk quality issues; too much testing and you theoretically risk shipping too slowly. The "right" amount is dependent on many factors.

Okay, I buy it, but I'm not sure how this is instructive.

This isn't directly instructive; rather, this should provide a north star for your testing efforts.

If your testing doesn't reduce risk, why are you doing it? Note that we're talking both about current risk (ensuring what you wrote works how you think it works) as well as future risk (ensuring that any future code you're writing doesn't regress existing test cases).

Risk reduction will, statistically, result in a reduction in adverse events. Risk in its simplest version may be described as "the probability that something bad might happen."

Perhaps the risk you are reducing has not materialized yet into anything bad. You are going from a 1% risk to a .01% risk. It's possible (but improbable) that you are writing tests to reduce a risk that has never materialized into an adverse event.

In any case, the instruction here is to measure the usefulness of your tests by the risk reduction factor.

"How does this testing work help us avoid something bad happening?" - When you are in your sprint refinement sessions, this is the question a good engineer will ask about a beefed up testing effort.

TDD and other reasons for testing

Remember, what we're talking about here is only one valid lens for the purpose of testing.

Another perfectly fine lens is to view testing as a creative tool. TDD (test-driven development) and other similar processes involve testing as a core part of the code writing, asserting that writing a test first jmay help ensure that the code written meets exactly the requirements.

It's worthwhile to ask why you would want to do this. Why would you want a developer to write only the code necessary to fulfill the testing requirements?

A few possible answers:

  • It creates a clarifying mechanism for the requirements
  • It ensures the developer is not spinning their wheels on things extraneous to the core requirements
  • It disambiguates the translation between requirement and implementation
  • It helps find product cases that may not be obvious when reading requirements directly

TDD is a solid creative process. Additionally, all of these are desirable from a business perspective because they reduce risk.

Wrap-up: Testing is about risk... but testing carries risk.

The most interesting insight I hope you gain from this article is that dogma surrounding testing may be dangerous, because dogma ignores risk modulations.

In other words, if you are testing to fulfill the "modern software testing requirements," you are missing the point.

Testing reduces risk, but it carries its own risk. Incorrect tests could instill a false sense of confidence in broken code.

Every activity you engage that involves code carries risk, and great engineers find multi-factorial ways to reduce that risk.

Written by Jonathan Cutrell, Engineering Manager at Guild Education and podcast host at Developer Tea. You can follow him on Twitter at @jcutrell.