'spyOn' is not defined.eslint(no-undef)

When testing Typescript files, ESLint might complain about some Jest/Jasmine functions (e.g. describe, test, it, onSpy, etc.):

'describe' is not defined.eslint(no-undef)

That happens even after installing the @types/jest package.

ESLint needs you to specify which environments your script will run:

// .eslintrc.yml
env:
  - jasmine: true
  - jest: true

Now, Jasmine and Jest types will be set as global variables and your linting will work again. :)

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