Which safety precaution is recommended liquid is being heated in a test tube?
Well, hold the test tube in a peg.........
Of course, I expect that you will be wearing (i) a pair of safety of spectacles or optical spectacles, and (ii) a lab coat. Such safety equipment are an absolute requirement for work in any laboratory. And hold the test tube in a peg. Use a soft Bunsen flame, and while you heat the tube, agitate it, to prevent bumping.
And of course you have to be aware of colleagues beside and opposite you. The test tube is taken from a wooden rack with the peg, and replaced in the rack.