Dissecting Complexity in Tests

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Learn about the most common reasons for complexity in tests, how it manifests, and how to deal with that complexity to produce elegant tests even for the most complex systems.

Artem Zakharchenko
Artem Zakharchenko
15 min
03 Nov, 2022

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Video Summary and Transcription

Today's Talk discusses complexity in tests and how to effectively deal with it. The speaker emphasizes the importance of testing critical user-facing paths and modeling tests from the user's perspective. They also highlight the significance of creating a testing setup that allows any test to run smoothly and the implicit testability of a well-designed system. The Talk explores the impact of choosing the right testing environment, the role of testing setup in mitigating complexity, and the importance of test structure and expectations. The speaker provides practical tips for tackling complexity in tests, such as keeping tests flat, using helper utilities, and splitting tests into separate files.

Available in Español

1. Introduction to Complexity in Tests

Short description:

Today, I would like to speak about complexity in tests. Complexity is destined to happen, but it's how we choose to deal with it that matters. Complexity in tests can come from the system being tested or from the tests themselves. When dealing with complexity from the system, start by testing the most critical user-facing paths. When it comes to testing, model it from the user's perspective and invest enough into testing setup.

Hello, everyone. My name is Artem, and I'm a software engineer at Kotlinbox. Today I would like to speak about complexity in tests, but before I begin, allow me to ask you a simple question. Have you ever felt like writing a test for a feature would require more time and effort than the feature itself? Well, like me, you have. Then, chances are you were dealing with one or maybe multiple ways how complexity may manifest in your code base.

But you shouldn't feel bad about it, because no matter how great engineers we are and what incredible code we write, complexity is destined to happen. It's fine. Complexity in itself is not the issue. It's how we choose to deal or not to deal with how it manifests what matters. And while complexity can be a broad topic, for the sake of today's talk, I would like to reference to it as a quality or state of being hard to write, understand, and maintain a test. And when it comes to complexity in tests, it can be divided into two main groups. It's the complexity that comes from the system that we're testing, and this can be really any code. A React component, a backend route handler, or a JavaScript library. And complexity that comes from the tests that we're writing.

So let's start from the system. And one of the most common ways how people stumble upon complexity, coming from the code that they test, is that they don't know what to test. I'm pretty sure you've been in this situation. You open an existing file and it seems to be doing everything possible in the universe, and you have zero idea how to even approach testing that. Well, there's actually a great rule you can follow in these situations. It is, whenever you're in doubt, start by testing the most critical user-facing paths. So if you're building an e-commerce product, well, starting a test strategy from a logging flow or a checkout flow makes the most sense. And if you're developing internal tooling or libraries, then start from those happy paths that users expect, and that should set you on the right track.

And then, when you know what to test, the next biggest problem, the next challenge, is how to test that. And I think very often, when we feel struggle with how to approach testing, it's because we may miss some sort of testing philosophy. And one of the most useful approaches that I've adopted over the years is testing like the user. What it means is that whenever you write a test, try to model it from the user's perspective. So your test actions that you perform would emulate the actions that that user would do with your software. And your assertions that you write actually reflect user expectations as the result to their actions. And then another thing that helps tremendously is when you invest enough into testing setup. And I feel this is very often overlooked and it's a shame, because the testing setup is perhaps one of the most important phases that deals with the complexity.

2. Complexity in Tests: Purpose and Testability

Short description:

The point of this phase is to create a universe where any test can run without problems. Each test should have a purpose, which is to describe the intention behind the system. Testing the testability of a system is an implicit test in itself. Poorly designed systems are hard to test, while well-designed systems make testing easier.

Because the point of this phase is to create this universe, this box, where any test can run, or any test that you want to write can actually execute without problems. And I'm going to talk about testing setup a little bit later into the talk.

Okay, so when you know what to test and how to test, you may be stumbling into another problem that is writing too many tests. And it may sound like a good thing at first, but it's not really because each test should have a purpose. And we often seem to forget the purpose behind testing in general.

And we write tests not to gain code coverage or to have the CI passing, although we want that. We actually write tests for a single reason. And that is we write tests to describe intention behind the system. Think about it. Whenever you write a piece of logic in your code, you have some sort of intention. You want that code to do something. But unless you have an automated test to validate that intention, you have no proof that your code works as expected.

So the next time you approach a test, ask yourself a question. Is what I'm testing actually related to the intention behind this code? Because if it's not, chances are you can drop this test and still lose no value in your testing setup.

And then the other thing is that, well, real world is quite more complex than that. And sometimes they're objectively complex systems, right? Or are there? Because one thing I love about testing is that a testability of the system is an implicit test in itself.

Now, what this means is that when you have poorly designed, poorly architectured systems, as a consequence, they're going to be really hard to test. And the opposite stands true also. Let me give you a few examples of how this manifests.

So in this get user function, we fetch user from the database. But we also fetch all the post for the user. And this feels that it doesn't belong here. Because now to properly test this function, we need to also mock everything related to posts. And this is a stretch. What maybe the proper approach here would be to split this one function into two and test them all in isolation, which would be much easier.

Another example is related to dependencies that our code introduces. Like this shopping cart controller. You can see that in the constructor, we're creating a new database connection. Well maybe that's not a good idea because to test this controller now, we need to implicitly mock this database constructor somehow. Why not just pass it as an argument to the constructor, do dependency injection, and thus allow us to test, for example, against the test database during testing, which would make this whole experience much easier.

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