Add snapshot test to dialog.test.js

[Darper]

The previous snapshot test was returning a false positive so it was deleted. This was caused by something in Portal.js, most likely ReactDOM.unstable_renderSubtreeIntoContainer() which has been replaced by ReactDOM.createPortal(). Please investigate.

[FacuRossi]

I would like to work in this test.

[Darper]

@FacuRossi Thanks! Let us know if you identify a solution. I spent a little time trying to implement ReactDOM.createPortal() but could never actually get any content to show up with the modal.