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Demystifying Testing

October 11, 2018


How to get from aimlessly testing or not testing at all to really understanding how and what to test.

In the next few weeks, you're going to get bonus emails from me as I prepare to launch the biggest undertaking I've ever taken. You'll love it. (Trust me, I've run the tests. 😉)

Many of you have messaged me, confused about where to get started with testing. Just like everything else in software, we work hard to build abstractions to make our jobs easier. But that amount of abstraction evolves over time, until the only ones who really understand it are the ones who built the abstraction in the first place. Everyone else is left with taking the terms, APIs, and tools at face value and struggling to make things work.

If there's one thing I believe about abstraction in code, it's that the abstraction is not magic, it's code. If there's another I thing I believe about abstraction in code, it's that it's easier to learn by doing.

Here's an example:

Imagine that a less seasoned engineer approaches you. They're hungry to learn, they want to be confident in their code, and they're ready to start testing. 👍 Ever prepared to learn from you, they've written down a list of terms, APIs, and concepts they'd like you to define for them:

  • Assertion
  • Testing Framework
  • The describe/it/beforeEach/afterEach/test functions
  • Mocks/Stubs/Test Doubles/Spies
  • Unit/Integration/End to end/Functional/Accessibility/Acceptance/Manual testing

So.........

Could you rattle off definitions for that budding engineer? Can you explain the difference between an assertion library and a testing framework? Or are they easier for you to identify than explain?

Here's the point. The better you understand these terms and abstractions, the more effective you will be at teaching them. And if you can teach them, you'll be more effective at using them, too.

Enter a teach-an-engineer-to-fish moment. Did you know that you can write your own assertion library and testing framework? We often think of these abstractions as beyond our capabilities, but they're not. Each of the popular assertion libraries and frameworks started with a single line of code, followed by another and then another. You don't need any tools to write a simple test. Here's an example:

1const {sum} = require('../math')
2
3const result = sum(3, 7)
4const expected = 10
5if (result !== expected) {
6 throw new Error(`${result} is not equal to ${expected}`)
7}

Put that in a module called test.js and run it with node test.js and poof, you can start getting confidence that the sumfunction from the math.js module is working as expected. Make that run on CI and you can get the confidence that it won't break as changes are made to the codebase. 🏆

Once you understand how the abstractions work at a fundamental level, you'll probably want to use them because hey, you just learned to fish and now you can go fishing. And we have some pretty phenomenal fish, uh, tools available to us. My favorite is the Jest testing platform. It's amazingly capable and fully featured and allows me to write tests that give me the confidence I need to not break things as I change code.

I'm really looking forward to what I'm creating for you. I think it'll help accelerate your understanding of testing tools and abstractions by giving you the chance to implement parts from scratch. The (hopeful) result? You can start writing tests that are maintainable and built to instill confidence in your code day after day.

Stay tuned. 🎣

P.S. Give this a try: Tweet what's the difference between a testing framework and an assertion library? In my course, I'll not only explain it, we'll build our own!

P.P.S. Set your alarms and tell your friends! On Friday Oct 19th my course goes on sale with early-bird pricing! It is HUGE. Like over 100 dense videos huge. Like ~5 dense hours of testing huge. Seriously, let people know. They don't want to miss this.

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Kent C. Dodds

Kent C. Dodds is a JavaScript software engineer and teacher. He's taught hundreds of thousands of people how to make the world a better place with quality software development tools and practices. He lives with his wife and four kids in Utah.