Testing Basics

Tests are code that we write, which we can run on our application code to make sure it’s behaving as we are expecting, and that any changes we’ve made don’t have unintended consequences. The goal of tests is to catch bugs before they get to the production site and break things.

As the scale of our application grows, it becomes more and more time-consuming and unwieldy to try to test every aspect of the site manually every time we make changes. Tests let us think through what we need to check to make sure a specific aspect or part of the site is working correctly, just the once while we are writing the test. From then on, the tests can be run routinely and we only have to think about it if one of them fails, telling us there’s a problem in a particular place.

If you are working on changes, or a new feature, please add appropriate tests and run the existing tests on your changes.

Tip

At the moment, there are many existing parts of the Boba codebase that need tests written for them. If you’re a beginner looking to get involved, writing tests for the existing code can be a great way to get a sense of how things work while contributing critical infrastructure.

We use a number of techniques and tools for testing different parts of the codebase. The following pages will outline how to write different kinds of tests, but many tests center around making an assertion that an outcome matches our expected outcome. A good example of this are Jest tests, whose assertions use the basic format:

expect(value).toBe(expectedValue);

We explicitly set the expectedValue to the outcome we want, and the value may be a value that was returned from a function we are testing, as in the basic example the Jest docs provide here, or a more complicated stand-in for the workings of our application, like an HTML element in the case of UI tests - which will be covered in detail on the next page, UI Tests with Jest and Storybook.