Eligible medical expenses include amounts paid for laboratory, radiological, or other diagnostic procedures or services together with necessary interpretations:
for maintaining health, preventing disease, or assisting in the diagnosis or treatment of any injury, illness, or disability;
for the patient; and
as prescribed by a medical practitioner.
Therefore, amounts paid for a COVID-19 test would qualify for the Medical Expense Tax Creditif the test was prescribed by a medical practitioner.
Note: COVID-19 tests, such as those for travel, would still need a prescription, even if they are mandatory.