Add unit test for `setSource` of Video
Add unit test for `setSource` of Video

Summary: The logic of getting supported video format from video source is a little complicated, add a unit test for this.

Reviewed By: mikearmstrong001

Differential Revision: D4954548

fbshipit-source-id: 2451bfb

ichengde/react-vr,ichengde/react-vr