In short, there is no email testing platform, like Email on Acid & Litmus, that can properly or thoroughly test video email campaigns, as they will not actually play the video during the tests.
That said, there are a few benefits they do provide:
It shows which email version will play a video, and which will show a static image by the image in the test.
They are a quick and easy way to review your email template across a wide range of email clients and devices.
Testing of video email should comply with the Playable compatibility list below:
Apple Mail: MP4, H.264, HEVC
Apple iPhone Mail (iOS12+): MP4, H.264, HEVC
Apple iPhone Mail (iOS11 & earlier): PNG
Apple iPad Mail: MP4, H.264, HEVC
Google Android: WEBP
Gmail: GIF
Outlook for Mac: MP4, H.264
Outlook.com: GIF
Outlook.com: WEBP
Outlook 2007-2016 for Windows: Static Image (<2% of consumer campaigns)
Samsung Mail: WEBP
Yahoo! Mail: GIF
Yahoo! Mail (Chrome): WEBP