Well, yes, in this situation random guessing would be very likely to provide an immediate check on the solution. (1x, 2x, 4x), as indicated in the video below,

Well, yes, in this situation random guessing would be very likely to provide an immediate check on the solution. (1x, 2x, 4x), as indicated in the video below, is not sufficient. It represents a subset of the values that are valid. Think of it this way. When asked to write a unit test, do you only test the positive outcomes? No, you test to make sure the failures are as you expect as well. Otherwise, you are likely to have what you think is a failure end up as a success.