The Poisson/Arago/Fresnel spot, which is a great example of the predictive requirement of science; this one being a binary condition. One implication of the hypothesis is that there will be a spot. Either there isn’t a spot, or there is, and that will or will not falsify the hypothesis.
“If Fresnel’s idea is correct, then the edges of a circular obstruction will act as sources of light waves. Most of these will cancel out and produce a shadow behind the object, as expected. But because the path length from the edge to the middle of the shadow is equal no matter where on the edge you start, the cancellation can’t happen and there has to be a bright spot right in the middle of the shadow. This is self-evidently bogus.”