This DEV-only field was added in 836331ba5f69f2cc53b273ec073fae116db14302 by @sebmarkbage but it's not being used anymore to my knowledge.
return <div>{context.lang}</div>;
    }
    Child.contextTypes = {lang: PropTypes.string};
    const el = document.createElement('div');
    ReactDOM.render(<Parent />, el);
    expect(el.textContent).toBe('en');
  });
  it('should work with arrow functions', () => {
    let Child = function() {
      return <div />;
    };
    
    
    Child = Child.bind(this);
    expect(() => ReactTestUtils.renderIntoDocument(<Child />)).not.toThrow();
  });
  it('should allow simple functions to return null', () => {
    const Child = function() {
      return null;
    };
    expect(() => ReactTestUtils.renderIntoDocument(<Child />)).not.toThrow();
  });
  it('should allow simple functions to return false', () => {
    function Child() {
      return false;
    }
    expect(() => ReactTestUtils.renderIntoDocument(<Child />)).not.toThrow();
  });
});