What are procedures in how to detect the viscosity of engine oils if it is still good to use?

Wow change your oil its not that much!What are procedures in how to detect the viscosity of engine oils if it is still good to use?
It is cheaper ot change oil than to repair an engine. Play it safe and change the oil sooner than later. It is not worth sending oil samples to a lab for analysis. It is not necessarily the Viscosity that wears out but the additives that encase the polutants in the oil that wear out.