Sample Jest test to mock localeString

mock-jest-locale.js

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',
        });
    });
});