The key checks for a diabetic foot ulcer are part of an exam rather than lab tests, and two of them matter most.
Your provider should check your sensation with a tool called a monofilament. A monofilament is a fine filament pressed against the skin to see whether you can feel it — the test for the loss of feeling that lets an injury go unnoticed.
Your foot pulses will also be checked. That one is about blood supply rather than feeling, which is the other half of why these ulcers form and fail to heal.
Both are part of regular care, not something saved for an ulcer. Regular exams with your provider are the best way to find out if you are at higher risk of foot ulcers due to your diabetes. The pulses in your feet and your reflexes should be checked at least once a year, and a provider should look for calluses, infections, sores, thick toenails, and loss of feeling anywhere in your feet.
Something is also done to the wound itself during treatment. During a debridement, the wound is probed with a metal instrument to see how deep it is and to see if there is any foreign material or an object in the ulcer. That is part of the procedure rather than a separate test.
At a wound care center the assessment is broader: the team will examine and measure your wound, check the blood flow in the area around the wound, figure out why it is not healing, and create a treatment plan.
If another test is arranged for you, the person arranging it is the one who can say what it is looking for.