"give a laboratory test' means what is an experiment you could perform to test for the presence of the gaseous products.
For example, in the case of CO2, you could bubble that into limewater (calcium hydroxide) and the limewater will turn milky. That is a test for the presence of CO2.
Another example, if you were testing for H2 gas, you could perform the pop test, as that is a laboratory test for hydrogen gas.
Hope that helps