accounts-frontend/tests/polyfills.test.js

import expect from 'unexpected';

describe('promise.prototype.finally', () => {
    it('should be invoked after promise resolved', () =>
        expect(new Promise((resolve) =>
            Promise.resolve().finally(resolve)
        ), 'to be fulfilled')
    );

    it('should be invoked after promise rejected', () =>
        expect(new Promise((resolve) =>
            expect(Promise.reject().finally(resolve), 'to be rejected')
        ), 'to be fulfilled')
    );
});