Testing after sale?

[John A]

Company A, which maintains a 401(k) plan, is sold to Company B, which also maintains a 401(k) plan, on July 1, 1998. The 401(k) plans will be merged May 1, 2000. Both plans are calendar-year plans.

Can anyone give me a general overview of how testing is done in 1999 and 2000? How is the former ownership of Company A treated (important for key employee definition, not used for HCE determination?)? Does company A's plan have to be tested for 1/1/2000-4/30/2000, or is it combined with the plan it is merged into and tested for all of 2000?

If this is too open-ended a question to ask here, does anyone know of an article that has been written on this issue? Thanks for any suggestions you might have!