Multiple Employer Plan- testing compensation

I have 2 companies that have a multiple employer plan. 

My question has to do with the compensation for the owner. I have an owner who owns 100% of Company A and 50% of Company B. This owner receives W2 compensation from both companies. I am wondering how I actually test the plan?

Do I have this owner in both companies' separate testings and give them an allocation in both? (They want to do the max) Or am i allowed to aggregate the compensation and only have the owner in one company's testing? I am leaning toward the first way as I feel they do need to be tested under each employer, but I cannot find a definitive answer anywhere.  

I do know that the 415 limit is based on the compensation the owner receives from both employers. 

The plan document should give you guidance.

You're skipping an important first step.  Is there a controlled group or affiliated service group?  It sounds like no Controlled Group, but what ASG?

If truly a multiple employer plan, then everything is run separate.  401k and comp from A are in one ADP test with Company A employees, and the same for B. (same for all other testing).

One 415 limit because its one plan.  You should be eligible for 2 415 limits IF you had 2 separate plans.

There is no controlled group or affiliated service group. From everything i have researched this qualifies as a truly multiple employer plan. 

They currently have a 401(k) profit sharing plan. They are looking at adding on a cash balance plan. As I did not set up the PS plan, I am stuck with what has already been established. 

Then I believe I should be testing this owner 2 times- once with company A and their compensation there and a second time with company B and their compensation at that entity. They can get an allocation in both companies under the one plan. And their 415 limit (on the CB side) is determined by a combination of all income from company A and company B. 

There is one 415 limit per plan even if it is a multiple employer.  Interesting though there are two 401a17 limits.  So if he has comp from Company A of $270K and Company B of $270K and the plan was a 3% SHNEC, he would get the SHNEC twice.

Obviously an actuary should chime in on how a multiple employer plan is handled in a cash balance scenario.  That would be interesting...

FYI, the basis for austin3515's conclusions is Treas. reg. 1.413-2(a)(3).