Using the custom utils file as described in the README where you re-export everything from react-testing-library and override the render method gives the following error:

TypeError: Cannot set property render of [object Object] which has only a getter

• react-testing-library version: 5.0.1
• react version: 16.5.0
• node version: 10.0.0
• npm (or yarn) version: 1.6.0

Relevant code or config:

// @flow
import * as React from 'react';
import { render } from 'react-testing-library';

const customRender = (node, ...options) => {
  return render(
    <div>{node}</div>,
    ...options,
  );
};

export * from 'react-testing-library';

export { customRender as render };

This is on create-react-app by the way (react-scripts@1.1.5)