test with enzyme a react component with context: return an empty object

I'm trying to execute a dummy test with enzyme over a component. the test is about to check the context. even though I'm writing the same code as enzyme's documentation the context is always empty.

import React from 'react';
import { shallow } from 'enzyme';
import Overlay from '../../../../app/components/Overlay/Overlay';


describe('<Overlay />', () => {
  it.only('retrun a context', () => {
    const wrapper = shallow(<Overlay />, { context: { foo: 10 } });
    console.log(wrapper.context());
    // expect(wrapper.context().foo).to.equal(10);
  });
})

the test's output is:

<Overlay />
{}
✓ retrun a context

where am I wrong?