What is 6-minute walk test to check if a person has low oxygen level in body?

Government has recommended the six-minute walk test for mild and moderate COVID-19 patients to check if they've low oxygen level. Patients are advised to walk around their room for six minutes with an oximeter attached to their finger. If the patient's oxygen saturation drops below 94% or he/she feels unwell during or after the test, they should consult a doctor.