How to mock window.navigator.language using jest

window.navigator and its properties are read-only, this is the reason why Object.defineProperty is needed to set window.navigator.language. It’s supposed to work for changing property value multiple times.

The problem is that the component is already instantiated in beforeEach, window.navigator.language changes don’t affect it.

Using Object.defineProperty for mocking properties manually will require to store original descriptor and restore it manually as well. This can be done with jest.spyOn. jest.clearAllMocks() wouldn’t help for manual spies/mocks, it may be unneeded for Jest spies.

It likely should be:

let languageGetter;

beforeEach(() => {
  languageGetter = jest.spyOn(window.navigator, 'language', 'get')
})

it('should do thing 1', () => {
  languageGetter.mockReturnValue('de')
  wrapper = shallow(<Component {...props} />)
  expect(wrapper.state('currentLanguage')).toEqual('de')
})
...