If the product has an expiry date it will be somewhere on the packaging (often on the bottom).
As a matter of interest I asked a chemist friend of mine about the expiry date on the foil sealed tablet type of test and he said that it is very unlikely that these actually go off. The chemicals used are designed to react in water so unless there is a lot of water leaking through the foil they will last for a lot longer than indicated.
HTH, Eddie