From Longman Dictionary of Contemporary Englishldoce_332_atest tubeˈtest tube noun [countable] 
HTa small glass container that is shaped like a tube and is used in chemistry → laboratory
HTa small glass container that is shaped like a tube and is used in chemistry → laboratoryExamples from the Corpus
test tube• Unknown to the teacher he had taken with him a test tube of the acid to test its reaction with lavatory paper.• In an invasive procedure, a doctor could extract one of her eggs and try to fertilize it in a test tube.• The father was a test tube baby.• In test tube and animal studies ABT-738 is the most potent anti-HIV drug to date.• Humans are inside the test tube to prevent the experiment from crashing, to divert the trials from overt crisis.• The rest of us humans are outside, but inside the test tube of planet Earth. 