How to check props of a DOM node in an unit test in React 0.14?

After upgrading React from 0.13 to v0.14.0-beta3, I got a lot of warnings like this in my unit tests:

Warning: ReactDOMComponent: Do not access .props of a DOM node; instead, recreate the props as `render` did originally or read the DOM properties/attributes directly from this node (e.g., this.refs.box.className). This DOM node was rendered by `Button`.

They are caused by my unit tests, for example:

it('should render to a <a> when href is given', function () {
    var button = TestUtils.renderIntoDocument(<Button className="amazon" href="#">Hello</Button>);
    expect(TestUtils.scryRenderedDOMComponentsWithTag(button, 'button').length).toBe(0);
    expect(TestUtils.scryRenderedDOMComponentsWithTag(button, 'a').length).toBe(1);
    expect(TestUtils.scryRenderedDOMComponentsWithTag(button, 'a')[0].props.href).toBe('#');
    expect(TestUtils.scryRenderedDOMComponentsWithTag(button, 'a')[0].props.className).toBe('amazon Button');
});

How do I fix this? Is there any recommended practice for testing DOM elements like this?