how to test the presence of oxygen?

Put a glowing splint into the test tube containg the gas. If the glowing splint relights, the gas inside is oxygen

Place a glowing splint in a test tube containing oxygen, if it re-lights, then oxygen is present.

You can use burning splint to test.You put it into tow test tube(There both are oxygen in the test tube), If one of the burning splint burns more time, it means this test tube has more oxygen.

you can test it with a glowing splint , if it relight . it means that oxygen is present