test-utils-refactor-1.jsx

const MemoryRouterWithInitialRoutes = ({ children }) =>
  <MemoryRouter>{children}</MemoryRouter>;

const customRender = (ui, options) => {
  return render(
    ui,
    {
      wrapper: MemoryRouterWithInitialRoutes,
      ...options
    }
  );
}

corrected -- thank you for bringing this to my attention!