declaring test dependencies explicitly

Do you want to request a feature or report a bug? Feature

What is the current behavior? The only obvious way to declare that x.test.js depends on (is related to) x.js is importing/requiring ./x in the test. Only with this import, Jest will run x.test.js when

• started with --findRelatedTests x.js or
• started with --watch/--onlyChanged and x.js has changed

What is the expected behavior? Some tests have dependencies that are not visible in the import tree. Examples:

• x.integration.test.js spawns a node x.cli.js subprocess. This case usually has a simple workaround - in x.integration.test.js: import './x.cli.js'; // implicit dependency via spawned node process It’s kind of ugly and needs a comment to explain why this import is needed.
• yaml-parser.test.js has a test resource file example.yml:

  import parseYaml from './yaml-parser.js';
  import { resolve } from 'path';
  test('yaml parsed correctly', () => {
    // parseYaml does some sort of fs.readFile('example.yml')
    expect(parseYaml(resolve(__dirname, 'example.yml'))).toMatchSnapshot();
  });
  

  This is harder to deal with - import './example.yml'; does not work because the runtime doesn’t know what to do with the file.

Solutions / Options

• is the side effect import workaround an acceptable way to do this or should Jest provide a more explicit way to declare dependencies?
• Would it be in the scope of Jest to provide a way to declare non-module dependencies? (second example)
• how would it look? jest.dependsOn('./x.js')?

[jeysal]

Oh, just tried it out, that actually works 🎉 I didn’t think of that before, thanks for the tip! For future reference: It appears that you also need to add the extension to moduleFileExtensions.

However, it only seems to affect --onlyChanged and --findRelatedTests, in --watch and --watchAll mode Jest does not watch the external resource. Maybe I’ll try to “fix” that then and submit a PR so the hidden require workaround works properly.

Edit (2018-05-06): Actually, watching does work as well, it only didn’t work because I tried it with a hidden file (dotfile), which Jest does not watch.

[SimenB]

I like the idea. Maybe we could use a docblock though, instead of a real API, similar to how we allow users to select test environment?