  Can one estimate the number of remaining faults in a software system? A
credible estimation technique would be immensely useful to project managers as
well as customers. It would also be of theoretical interest, as a general law
of software engineering. We investigate possible answers in the context of
automated random testing, a method that is increasingly accepted as an
effective way to discover faults. Our experimental results, derived from
best-fit analysis of a variety of mathematical functions, based on a large
number of automated tests of library code equipped with automated oracles in
the form of contracts, suggest a poly-logarithmic law. Although further
confirmation remains necessary on different code bases and testing techniques,
we argue that understanding the laws of testing may bring significant benefits
for estimating the number of detectable faults and comparing different projects
and practices.
