Vladimir wrote:

> also do not forget testing blindeness effect and use distinct values
> for a, b and c which when used will not lead to a correct result even
> in faulty implementation.

How faulty an implementation?

For example sin(5) should not return 120 but a sin function that is
infact a factorial function would return this answer. Ok this is a very
big error but I've seen some programmers come close.

For any function there can be an implementation that gives a dumb
answer:

def sin(a)
    return 120
end

Testing, blackbox stylee, for bad implementations leads to, well,
infinite tests! Ever heard of the 'knocking demon' hypothesis.