Testing a terminating plan

When testing a 401(k) plan that has made the determination to terminate the plan. Would the plan year end date for purposes of non discrimination testing be the date the termination resolution was signed?

Here is a example:

The company is going out of business and the resolution to terminate the plan was signed in March. Would non discrimination testing be run from 1/1 - March (the plan is calendar year) or would the compliance testing run from 1/1 - the date the assets are at zero?

When did compensation and contributions cease? I think that would be the relevant end date for testing.

In other words, what does the Corporate resolution say is the effective date of the plan termination ?