Test Kitchen: A Recipe for Good Tests

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Most of us have heard that tests should be isolated, composable, or deterministic, but what does that mean in practice? How do you write a good test and how does the rest of your codebase change once you do? What effect does it have on your developer experience? In this talk I'll walk through a hand full of properties good tests have, show how we can write tests that follow these guidelines in JavaScript, and discuss when to consider bending the rules a bit.

Iris Schaffer
Iris Schaffer
29 min
14 May, 2021

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Video Summary and Transcription

Iris, a software engineer, shares her cooking journey and invites others to share recipes on Twitter. She discusses testing guidelines, emphasizing the importance of automated tests that inspire confidence and run all the time. Iris provides tips for faster and more effective testing, including running tests in parallel and focusing on behavior. She also highlights the importance of making tests robust, readable, and maintainable. Finally, Iris emphasizes the value of testing, predictive tests, and audience preferences in software development.

Available in Español

1. Introduction to Iris and her cooking journey

Short description:

I'm Iris, a software engineer from Austria, currently living in London. During the pandemic, I've been cooking a lot and trying different recipes from around the world. If you have any interesting recipes or dishes from your home country, please share them with me on Twitter.

My name is Iris, which is Greek for rainbow. I'm a software engineer from Austria, but I've lived kind of all over Europe, and I currently call London my home. And the reason I chose a cooking related title for my talk is that I haven't done much else since the pandemic started. So from homemade pasta, bread, and pizza, to theme nights like West Africa, Sri Lanka, Mexico, or my own Vamana, I've pretty much made it all over the last year. So if you have any interesting recipes or anything from your home country that you'd like to share with me, please send them to me on Twitter my hand is right up there.

2. Testing Guidelines and Automation

Short description:

And when I don't cook, I develop products for our users at Spotify. We are one of the world's biggest audio streaming services with over 70 million tracks and almost 350 million monthly active users. Let's dive into the guidelines. Kent Beck lists 12 properties of tests. Tests should inspire confidence, enabling you to refactor your application without fear. Tests should be automated and run without human intervention, allowing teams to work autonomously and iterate quickly. Automated tests should run all the time, from development to deployment.

And when I don't cook, I develop products for our users at Spotify. In case you're not familiar with Spotify, we are one of the world's biggest audio streaming services with over 70 million tracks, including 2.2 million podcast titles. And with almost 350 million monthly active users, you can imagine the quality and testing practices are taken very seriously here.

So let's dive right into the guidelines. Do you remember the slide? Where did I have all of the adjectives from? The truth is I have not spent nearly enough time in this space to come up with a comprehensive list of properties a test should have. So I instead leave that up to you know, someone who has, like, Kent Beck. In a Medium post in 2019, Kent lists 12 such properties. But what do they mean in detail? Let's look at them one by one and see how we can use them to write better tests and code in JavaScript and React.

Let's start with what I believe is the most important one of all of these and probably the only one on the list that I would never, ever compromise on. Tests should inspire confidence. Confidence that your application works. Let's think about an example here. You want to refactor a central part of your application. Maybe you want to, I don't know, go from state management and Redux to context API. Or maybe you want to use a script to migrate your codebase from JavaScript to typescript. Let's not think about automated tests for a moment, but how you would generally go about doing a big change like that. Would you just change the code and deploy it? At least I would be extremely careful and thoroughly test each part that I'm touching before deploying because that manual testing is what gives me the confidence that I didn't just break the application. And that is exactly what testing is all about. Inspiring that confidence and enabling you to vigorously refactor your application without the fear of breaking it.

And that perfectly brings me to the second point, tests will be automated and run without human intervention. Say you work on a bigger project where several teams are in different components in your application. You now want to change a single line in the base button component that all other teams use. Not only will it take a lot of coordination from all these different teams, the testing will also have to be a joint effort because you might be able to do the changing button, but you don't know how it is used in all different places all over the application. And it's simply not feasible for this and any other seemingly small change to have to go through manual testing for each release because the coordination and time effort are just too high and grow with the scale of the application as well. So if you want to enable teams to work autonomously and iterate quickly in their part of the application at a certain size, you can only achieve this through automation. That brings me back to the question, when should automated tests run? And the answer is basically all the time. During development, it helps to have a quick feedback loop to at least run unit tests in watch mode so that you can find bugs early before even pushing any code. Once you're ready to merge your changes, all your tests should run on that branch. Then after merging, before deploying to production, your tests should be run on the main branch as well. This includes unit tests, integration tests, and if possible end-to-end tests if you have a way of running them on this branch.

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