describe('optional param syntax', () => {
      test('keeps the old route parameters if no new value is given', () => {
        const ownProps = { routes: [{ path: 'group(/:groupId)' }], params: { groupId: '1' } };
        const buildRoute = createBuildRoute(ownProps);
        expect(buildRoute('sessions', { param: 'param1' })).toBe('/group/1/sessions');