I haven't used PBT much, but I did once get a lot of mileage out of it, which was when I was implementing a fairly gnarly edit-distance algorithm. In that case,

I haven't used PBT much, but I did once get a lot of mileage out of it, which was when I was implementing a fairly gnarly edit-distance algorithm. In that case, I used PBT to check that the required properties of metric functions (d(x,x)=0, d(x,y)>0, d(x,y)=d(y,x), d(x,z) <= d(x,y)+d(y,z)) held for my implementation, which helped shake out a fair few stupid implementation mistakes.