Delayed testing

Hi. I need to know what the employer’s obligations are for the following situation, which is theoretical at this point but I want to be prepared as it may become real shortly. Scenario: We request that a worker submit to a drug test due to reasonable suspicion of substance use on site and they refuse on that date, but they then approach us with a clean test done days later on their own time. Are we allowed to refuse to consider that test as proof of compliance with our policy?