Sometimes a test can't be done: the area's flooded, the engineer's off sick, the machine's in use. Record that with Couldn't test in the Test Runner.
You'll be asked for
Why it couldn't be done.
What will be done differently next time ("take an umbrella", "book access a week ahead").
A new date to try again.
What happens
The test stays on the board, marked attempted.
It still counts as untested, and keeps its original due date.
If it goes overdue, Conform asks why, and that can become a finding.
If the control no longer applies at all (the machine's been sold), that's a matter for the assessment, not the test. Raise it with the unit's assessor.