Cuvette
A cuvette is a kind of laboratory glassware, usually a small tube of circular or square cross shape, closed at one end and open at the other, made of plastic, glass, or optical grade quartz and made to hold samples for spectroscopic experiments.  The best cuvettes are as clear as possible, without impurities that might affect a spectroscopic reading.  Like a test tube, a cuvette may be open to the air on top or have a glass or other material to close it.