Minimum coverage testing

[7806akp]

How does the minimum coverage test apply to 401(k) and (m) portions of a plan? Reg sec. 1.410(b)-8(a) seems to provide that the 401(k)/(m) portions must pass the test as of the last day of the plan year, but Rev. Proc. 93-42 sec. 3.08 provides that a plan with salary reduction and matching contributions can use snapshot testing (as of any day of the plan year) to comply with the minimum coverage testing requirement. Which day (last day or snapshot day chosen by employer) should be the testing day?