tgui/docs/writing-tests.md

You can now write and run unit tests in tgui.

It's quite simple: create a file ending in .test.ts or .spec.ts (usually with the same filename as the file you're testing), and create a test case:

test('something', () => {
  expect('a').toBe('a');
});

To run the tests, type the following into the terminal:

bin/tgui --test

There is an example test in packages/common/react.spec.ts.

You can read more about Jest here: https://jestjs.io/docs/en/getting-started

Note, that there is still no real solution to test UIs for now, even though a lot of the support is here (jest + jsdom). That will come later.