99 Honda Accord-Check engine light and getting smogged?

I have a 99 Honda Accord. My check engine light came on recently and my coworker hooked up the code reader (or whatever its called) and got code P0420 which is "catalyst system efficiency below threshold". I read that it could be an oxygen sensor OR catalytic converter. My coworker cleared the code and I purchased the sensor. He cleared the code Friday, and it hasn t come back on as of yet. I have to get my car smogged for the registration. My coworker said I should do it now while the light is off. He said if the check engine light was going to come back on, it would have come on very soon after it being cleared. Does anyone know if this is true? I don t want to take it and have it fail, and I have the sensor so I could have a coworker replace it before I get it smogged. I live in California, I think that our emission standards are Really high here. Should I attempt to get it smogged while the light is not on?

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