Testing

This post goes through approaches to asserting on the scroll position. First we’ll see how to assert that we’re at the top of the page. Next we’ll look at 2 approaches to assert that we’ve scrolled to an element. The examples for this post are available at ...

In a recent project I needed to fail/pass some AVA if a runtime environment variable was unset or empty. Here’s how I solved this issue. AVA is a test runner for Node.js with a concise API, detailed error output, embrace of new language features and process isolation that l ...

This article explains how to manage video content with HTML and JavaScript. Video content has become a significant part of Internet use, and it plays a large role in user experience. The ability to effectively include video content in your sites can help you improve user experien ...

Between test runs we need mocked/spied on imports and functions to be reset so that assertions don’t fail due to stale calls (from a previous test). This is a way to mitigate what little statefulness is in the system. In unit tests of complex systems, it’s not always ...

Where other JavaScript testing libraries would lean on a specific stub/spy library like Sinon - Standalone test spies, stubs and mocks for JavaScript. Works with any unit testing framework., Jest comes with stubs, mocks and spies out of the box. This post looks at how to instanti ...

It’s possible to do partial matches on Arrays and Objects in Jest using expect.objectContaining and expect.arrayContaining. expect has some powerful matcher methods to do things like the above partial matches. Using Jest at an advanced level means using tools like these to ...

When testing code with Jest, it can sometimes be useful to fail a test arbitrarily. This post goes through a few scenarios where that might be useful and how to fail a Jest test explicitly/in a forced manner. It also presents more idiomatic Jest patterns that could be used interc ...

JavaScript import/require module testing do’s and don’ts with Jest The example repository is available at github.com/HugoDF/mock-spy-module-import. This post goes through how to achieve different types of module mocking scenarios with Jest. From simple Import interc ...

When debugging or writing units tests with Jest it can be useful to specify a single file or test to run or to exclude a specific failing test for the Jest run. This post goes how to skip and exclude a single test, a whole Jest test suite and a whole Jest test file using the CLI ...

By default Jest runs tests in parallel with a “a worker pool of child processes that run tests” (Jest CLI docs). As per the Jest documentation, running tests in sequence (serially), can be helpful for debugging purposes and for test run performance reasons. ...