The Road to 100% test coverage

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NodeConf EU 2023 100% test coverage The road to ruyadorno.com

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The road to 100% test coverage Ruy Adorno Senior Software Developer working at Google Node.js TSC NodeConf EU 2023 ruyadorno.com

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TOC Setup the work environment for the workshop Understanding test coverage Techniques Questions / Consultation The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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Setup Install node 20 (or 18): https://nodejs.org/en/download Open your terminal, navigate to a suitable folder, e.g: cd ~/tmp/100-workshop Run the workshop generator: npm init @ruyadorno/100-workshop@latest Run npm install and tests: npm it The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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What’s in it? The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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Give it a try: List all LTS releases: node cli.js --filter=lts Last month’s releases: node cli.js --recent=month Only return the resulting count: node cli.js --count The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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What is a test A way to programatically confirm your program does what you think it does. If your tests are also a program, what validates that program? Surprise: It’s you, the developer! The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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Test Coverage Tracking coverage is sort of a meta test It tracks what parts of the program are executed Gives you a hint of how much of a test it really is Definitely does not prove that either the source code OR the test code are good The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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100% Test Coverage It means you covered all lines, functions and statements Still not enough, 100% code coverage does NOT mean 100% of features tested Gives you super powers The road to 100% test coverage NodeConf EU 2023 ruyadorno.com 🦸

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Notice: This workshop has a cheat code available To quickly complete a step, it’s possible to use the same generator ran to create the boilerplate. Run the generator using the step option. In this example we’re using the generator to complete Step 1: npx @ruyadorno/create-100-workshop --step=1 The road to 100% test coverage NodeConf EU 2023 ruyadorno.com ⚠

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Step 1 Let’s add an initial test to the main index.js module! The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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The road to 100% test coverage NodeConf EU 2023 ruyadorno.com ./test/index.js ۪ ۪ $ npx @ruyadorno/create-100-workshop --step=1 ./src/index.js

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Step 2 Let’s avoid the network request The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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The road to 100% test coverage NodeConf EU 2023 ruyadorno.com ./test/index.js ۪ ۪ $ npx @ruyadorno/create-100-workshop —step=2

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Let’s visualize better the coverage results: Opens an html-based interface in your default browser: npm t -- --coverage-report=html The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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Step 3 Let’s add tests for format-count.js The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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The road to 100% test coverage NodeConf EU 2023 ruyadorno.com ./test/format-count.js ۪ ۪ $ npx @ruyadorno/create-100-workshop —step=3

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The road to 100% test coverage NodeConf EU 2023 ruyadorno.com 🤩

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Step 4 Let’s refactor and add tests for filter-recent.js The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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The road to 100% test coverage NodeConf EU 2023 ruyadorno.com ./src/format-recent.js ۪ ۪ $ npx @ruyadorno/create-100-workshop —step=4 ./src/date.js

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The road to 100% test coverage NodeConf EU 2023 ruyadorno.com ./test/format-recent.js ۪ ۪ $ npx @ruyadorno/create-100-workshop —step=4

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The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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Step 5 Let’s add tests for filter-npm.js The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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The road to 100% test coverage NodeConf EU 2023 ruyadorno.com ./test/filter-npm.js ۪ ۪ $ npx @ruyadorno/create-100-workshop —step=5

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The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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Step 6 Let’s add tests for filter-booleans.js The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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The road to 100% test coverage NodeConf EU 2023 ruyadorno.com ./test/filter-booleans.js ۪ ۪ $ npx @ruyadorno/create-100-workshop —step=6

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The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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Step 7 Let’s add tests for the output.js module The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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The road to 100% test coverage NodeConf EU 2023 ruyadorno.com ./test/output.js ۪ ۪ $ npx @ruyadorno/create-100-workshop —step=7

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The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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Step 8 Let’s test retrieve-nodejs-versions.js The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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The road to 100% test coverage NodeConf EU 2023 ruyadorno.com ./test/retrieve-nodejs-versions.js ۪ ۪ $ npx @ruyadorno/create-100-workshop —step=8

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The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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Step 9 Let’s add the missing test to the index.js module The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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The road to 100% test coverage NodeConf EU 2023 ruyadorno.com ./test/retrieve-nodejs-versions.js ۪ ۪ $ npx @ruyadorno/create-100-workshop —step=9

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The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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Awesome Job! The road to 100% test coverage NodeConf EU 2023 ruyadorno.com 👏

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Less than 100% If you can’t delete it, you should probably write tests for it so that you can maybe know what it does It means there are entire components of your application without tests What kind of program needs no test at all? The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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Less than 100% Would you rely on a module with no tests? A 95% test-covered program is two parts: the covered part and the uncovered part The uncovered part is a module with no tests The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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Bene fi ts Testable code === maintainable code Full coverage forces you to look in dark corners Investigation process tends to uncover bugs Let you focus on what you’re good at while the computer keeps track of everything else you’ve already checked The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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Human aspect Going from 98% to 96% looks and sounds ok Going from 100% to 99.5% is a huge loss! It feels great to see all these rows of 100% covered modules It’s addictive 😁 and will trick you into being a better developer! The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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Extra costs Full coverage adds up-front to development cost In return it reduces the incidence of bugs, and the costs of changing a program Less technical debt! The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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Extra costs Full test coverage will not prevent all bugs, what it does is gives you the power to fix these bugs more efficiently What about TypeScript and eslint preventing most errors already? Soon after you wrote types you no long knows what the code is actually supposed to do The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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Bad tests People will write bad tests with less than 100% coverage too The solution is to write better tests, and more easily tested components, not to accept untested code Only testing the happy path is the equivalent of “works on my machine” The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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Levelling Up Limit coverage values to only account for a test written for a specific module Avoiding accidental coverage, e.g: a base class method from module A gets coverage when run from module B tests tap supports it out-of-the-box with its coverage-map config option The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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Techniques Tests with long assertion output that have to be updated on every change? Use snapshots for that, save them in git, review the diff. Have to mock the whole world to hit a buried path? Refactor it into a discrete submodule, and only mock that module once. You’re now writing better code. The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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Techniques Full coverage isn’t about writing code with more tests, it’s about writing code that is more testable. Monkey-patching and other “bad” software development practices are usually totally fine in tests! The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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Techniques Things that really cannot be tested for some reason? Use ignore comments. This is an explicit (and well-documented, it’s going to live there with your code) way of opting-out of coverage for a very valid reason. The road to 100% test coverage NodeConf EU 2023 ruyadorno.com

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End of the workshop Questions? Consultation time. The road to 100% test coverage NodeConf EU 2023 ruyadorno.com ⏰

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The road to 100% test coverage Isaac Z. Schlueter node-tap author & author of the original “99% is not enough” talk this workshop is based from. NodeConf EU 2023 ruyadorno.com Special thanks to:

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The road to 100% test coverage Ruy Adorno Linkedin: /in/ruyadorno @ruyadorno @[email protected] @ruyadorno.bsky.social NodeConf EU 2023 ruyadorno.com Thanks! Find me at: