Mock toLocaleString in Jest
PhantomJS doesn't support multiple locale. Here is a way to mock them in tests.
Wed, 01 Feb 2017
We had to use toLocaleString with a specific country-code. toLocaleString('de'). This works perfectly in all the browsers. However, not in jest tests.
Our Jest tests were running with --env=jsdom I got to know that jsdom and phantomJS aren’t supporting multiple locale implementations.
PhantomJS support locale-specific.
So, the only solution I found is to mock these methods and test rest of the logic. Here is a sample mock behaviour.
import * as helpers from '../src/helpers';
describe('formatDate', () => {
it('should invoke localString implementation to format date ', () => {
const localStringMock = jest.fn();
const mockDate = { toLocaleString: localStringMock };
helpers.formatDate(mockDate);
expect(localStringMock).toHaveBeenCalledWith('de-DE', {
year: 'numeric',
month: '2-digit',
day: '2-digit',
hour: '2-digit',
minute: '2-digit',
});
});
});Note: This behaviour is applicable for toLocaleDateString() toLocaleTimeString()