How to stub exported function in ES6?

Ouch.. I found solution, so I use sinon to stub and import * as foo from 'foo' to get object with all exported functions so I can stub them.

import sinon from 'sinon';
import cap from 'cap';
import * as foo from 'foo';

sinon.stub(foo, 'bar', m => {
    console.log('confirm', m);
});

describe('cap', () => {
  it('should bar', () => {
    cap('some');
  });
});