ESM Unit

Spec sheet

Purpose

ESM Unit is a unit testing tool for native ECMAScript modules in web browsers.Read 8 Oct 2026 · github.com

Intended users

The stated use case is developers who need to unit test native ECMAScript modules in web browsers.Read 8 Oct 2026 · github.com

Integrations

The README recommends Sinon for stubbing, mocking, and assertions against mocks.Read 8 Oct 2026 · github.com

Support

The project README invites users to open an issue or pull request and says it welcomes contributions.Read 8 Oct 2026 · github.com

License

The repository license identifies the software as Apache License 2.0 and states that it is provided without warranties or conditions.Read 8 Oct 2026 · github.com

Headquarters

Mountain View, California, United StatesRead 28 Sep 2026 · github.com

Founded

1983Read 28 Sep 2026 · github.com

Maker

Intuit’s GitHub organization lists Mountain View, CA as its location.Read 8 Oct 2026 · github.com

Assertions and mocks

It includes built-in assertions, supports other assertion libraries loadable as browser ECMAScript modules, and recommends Sinon for stubs and mocks.Read 8 Oct 2026 · github.com

Browser execution

It runs tests in real browsers without bundling or transpilation.Read 8 Oct 2026 · github.com

Browser support

The README shows running tests in Chrome, Firefox, and Safari; headless mode is supported only in Chrome and Firefox.Read 8 Oct 2026 · github.com

Coverage

It supports per-file code coverage reports and configurable coverage thresholds.Read 8 Oct 2026 · github.com

Debugging

A failed test can be rerun on its own by clicking “Isolate” in the browser window.Read 8 Oct 2026 · github.com

Distribution

The README instructs users to install ESM Unit with npm as a development dependency.Read 8 Oct 2026 · github.com

No build step

It runs tests in browsers without bundling or transpilation.Read 8 Oct 2026 · github.com

Notable limitation

Code using JSX or imports that are not native ES modules from local relative paths must be converted before running.Read 8 Oct 2026 · github.com

Requirements

ESM Unit requires Node 18 LTS or later and test code that runs in current browsers as native ECMAScript modules without transpilation.Read 8 Oct 2026 · github.com

Test isolation

Each test file runs in an isolated iframe with its own window and DOM document.Read 8 Oct 2026 · github.com

Watch mode

The --watch option reruns tests when files change, and cannot be used at the same time as --debug.Read 8 Oct 2026 · github.com

Where Specifiction places it

• JavaScript Testing Frameworks#15 of 237.3