A test tube, also known as a culture tube or sample tube, is a common piece of laboratory glassware consisting of a finger-like length of glass or clear plastic tubing, open at the top and closed at the bottom. Test tubes are usually placed in special-purpose racks. A test tube, also known as a culture tube or sample tube, is a tubular equipment made of glass or plastic. Further, the tube has an opening at one end and is sealed at the other end. The sealed end is most of the time circular, flat, or conical.