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To measure INL/DNL you need a huge number of samples that is usually impractical in simulations.
At any rate, I would use the sinewave method: the input signal has an "almost full-scale" input at a frequancy given by f=fclk*D/N, where fclk is your clock frequency (say, 100MHz), D is an odd number (151) and N is the sample length (8192), so f=1.8432617MHz. Choose D so that your test frequency is close to your desired frequency.
At this point you can give the ADC output to a matlab script like dnl_inl by Boris Murmann and you got it!