Oxygen Sensor

[solanog]

Is there a simple way to test the Oxygen sensor? I'm not a mechanic and have no idea of how to do it.
I asked because my Accord lx 1990 has new spark plugs, air filter etc and fuel economy is dropping. It also has become over some time sluggish, throttle response is sometimes O.K but others is very slow and the car hesitates to accelerate at low RPMs on high RPMs this hesitation is less noticeable. So I suspect of the oxygen sensor.
Any simple advice if it exists will be greatly appreciated, I don't want to spend a lot of money on a sensor and discover that it was not what was wrong. No check engine light as of now. I have replaced that thing a couple of times before, both gave check engine codes, one time was 42 I think, fuel delivery (supply) system and the other was O2 heater or something similar.
At least I own a digital voltimeter which I think is needed for testing the O2 Sensor.

Thanks