Instant feedback arrives for JavaScript code testing

Wallaby.js tool leverages parallel test execution and dependency analysis to provide for quick running of tests

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Developers looking for quick results when testing JavaScript code could have a solution with the Wallaby.js test runner tool, a code coverage technology intended to offer nearly immediate reporting of results.

The tool uses techniques like dependency analysis to only test code affected by changes, and parallel test execution to run tests as quickly as possible, according to the Wallaby website. "Wallaby.js automatically runs your JavaScript tests as you write your code," project founder Artem Govorov said in an email. "It reports code errors with navigable stacks, test expectation errors, code coverage, test execution time and much more." Feedback is delivered to the code editor, to the line of code being edited.

"My major goal was to create a tool that would allow [me as a developer] to get an instant feedback from my tests and right in my editor, just as I type my code, even if I have thousands of tests," said Govorov, who has worked as an independent contractor at JetBrains. "Existing test runners can either run some manually selected tests or all of the tests, and it may be time-consuming. Wallaby.js in its turn is using a sophisticated technology to automatically calculate and run the minimal required number of tests affected by your code changes." Wallaby.js, however, can work alongside testing technologies, such as Mocha, Jasmine, and QUnit

Although it's a commercial project, the tool is currently usable for free. The 1.0 version released late last month can test both Node.js and its recent fork, io.js. ECMAScript 6 also is supported, along with React JSX dialect support, JavaScript file configuration, and Require.js.