The sample has to represent the population, that's fundamental. If the sample is so small that it can't characterise the population distribution, then you have a problem anyway. If you're measuring a events that happen 1% of the time (or 99% of the time), a sample of 100 is not nearly enough.
If you chose an appropriate non-parametric test to cover an unknown distribution with a small sample, it maybe would have zero power (impossible to give a significant result)
The sample has to represent the population, that's fundamental. If the sample is so small that it can't characterise the population distribution, then you have a problem anyway. If you're measuring a events that happen 1% of the time (or 99% of the time), a sample of 100 is not nearly enough.
If you chose an appropriate non-parametric test to cover an unknown distribution with a small sample, it maybe would have zero power (impossible to give a significant result)