Does a profit sharing plan that provides a flat 5% contribution to all participants have to be tested for nondiscrimination?

No. But it needs to be tested for coverage. If by "participants" you include 1) everybody in the company (where for this purpose "company" is the controlled group); 2) those who terminate before the end of the year and 3) those that work less than 1000 hours in the year, then it passes coverage automatically, too. If no to any of the three, then it still needs to be tested for coverage.

Thank you Mike Preston

Depends on what the definition of eligible pay is . . .