Sorry ... posted too early. OK ... here's a better answer.
During the "test week", there's only one evening magic hour (Wed) at MK, so if it does affect Wishes, you do have several other options for days that you're in MK that week. Wishes is scheduled nightly throughout that week, so you'll have other nights available. Same is true of Fantasmic. The three "extra hours" will vary in the evening, depending on when the park was scheduled to close.
Guests who are not eligible for the Extra Magic Hours benefit will be directed to the park exit upon park close. In order to stay in the parks for EMH in the evening, you'll need a wristband, which you need to get prior to park close, by showing your resort ID.
For planning purposes, here's the schedule of EMH days from May 9-22:
Sunday - Epcot (evening)
Monday - Disney's Animal Kingdom (morning)
Tuesday - Disney-MGM Studios (evening)
Wednesday - Epcot (morning); Magic Kingdom (evening)
Thursday - Disney's Animal Kingdom (evening)
Friday - Magic Kingdom (morning)
Saturday - Disney-MGM Studios (morning)
