The recent changes to the JavaScript diff fragment rendering code

changed how state was stored and made collapsing an optional state.

That change neglected to update the unit tests accordingly for the new

storage and collapsible options, which this change fixes. It also

explicitly sets the expanded state for styling purposes, which wasn't

set before (and wasn't technically needed but might be needed down the

road).

Unit tests pass.
Tested diff fragments in expanded entries, collapsed entries, and in

the Review Dialog.