JSJ 411: Unit Testing Jest with Daniel Caldas

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Daniel Caldas is calling from Singapore. He currently works as a software engineer for Zendesk and has also worked in Portugal and Germany. He has worked primarily on the frontend with Node and JavaScript. He talks about his experience testing JavaScript, how he got started with Jest, and why he likes it. Daniel finds Jest very easy to use and straightforward. He likes that Jest has a single reference page for documentation. He feels that Jest is largely complete out of the box and has only made a small add on to get rid of Boilerplate in some tests.

Daniel explains what a snapshot, how they work, and why he prefers fixtures over factories. He gives tips on how to set up your tests so that they are easy to follow. He finds it helps to structure your scenarios in the fixture description. He talks about gotchas in Jest. While Jest is largely easy to use, Jest has been around for a while and breaking changes do happen. It’s important to check what version your code base is using. While there are a lot of free sources around Jest online, he advises listeners to stick as close to the official documentation as possible, or to people associated with Jest, and to read recent stuff. As for conventions, Jest has pretty much everything out of the box and the built in conventions make it easy to navigate any project that uses Jest.

Daniel talks about some of the features available in Jest, converting observables into promises, and tricks he has used to make tests easier to put together. He talks about his method for keeping his mocks and stubs straight. He advises listeners to have some organizational rules, such as starting the imports alphabetically, and to always follow those rules. He talks about how he runs tests and what environments he uses. While Jest is normally used for unit testing, Daniel has also used it for end to end tests, and he talks about his experience with an open source project doing both types in Jest. Daniel concludes the show by advising listeners starting with JavaScript and frontend, don’t think too much about the library you’re going to use because you’ll probably end up using Jest. It’s more important to have unit tests and a proper testing framework at the beginning than anything else. He also invites listeners to check out his open source work on Github.