Meaning of “test tube” - Learner’s Dictionary

test tube

noun [ C ] us uk
Scientists must test the drug before it goes on the market.The scientists only discovered the side effect while testing the drug on patients.We need to test the device in order to ensure it is safe.Each car is tested in a crash situation.Only by testing the software can we discover if it works properly.

a glass tube that is closed at one end and is used in scientific experiments

(Definition of “test tube” from the Cambridge Learner’s Dictionary © Cambridge University Press)