If you're buying parts in quantity, you probably want to "spot-check " each lot, i.e. take ~10% (fewer if the lot is large but at least a dozen or more) of the components you receive and run them through a thorough test to ensure that they (1)behave as nominally expected and (2) tolerate all the specified stresses. This means that you raise and lower the ambient temperature, vary the supply voltage at both high and low frequency, and do all sorts of other things to the device to ensure that it still behaves as specified under the most extreme conditions that it is supposed to tolerate.

Merely checking to see whether an inverter inverts or an amplifier amplifies is not enough. If any components fail this sort of testing, the entire lot should be rejected and returned to the distributor. Some people believe that, if you only use three of four gates in a package, you don't need to test the unused gate. That is wrong, as a failed gate indicates a failed device. If an LCD doesn't display the letter 'A' it is defective, even if you don't use the letter 'A'. If your MCU doesn't properly execute ACALL, it is defective, even if you don't use that instruction.

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