Re: How to unit test random seeds?
Daniel Dyer wrote:
On Thu, 20 Dec 2007 03:22:01 -0000, Patricia Shanahan <pats@acm.org> wrote:
Eric Sosman wrote:
Patricia Shanahan wrote:
I have an application that uses two random number generator instances.
The input parameters can specify the seed for either or both of
them. If
a seed is not provided in the input, I use a SecureRandom's
generateSeed().
I can obviously unit test the processing of specified seeds. The
problem
is how to test my use of generateSeed(). Any ideas?
Idea (maybe not the greatest, and definitely not original):
Some features of a program are amenable to testing, others are
better suited to inspection. If your test proves that "no seed"
does in fact wind up using SecureRandom, just assume SecureRandom
does its job properly.
I do assume SecureRandom does its job properly. The question I would
like to test is whether I am using it correctly, as well as the more
general question of how to test one's use of pseudo-random features.
I'm not sure that I am certain what you are asking. Do you want to test
under which circumstances your code makes calls to generateSeed()? In
other words, do you want to assert that generateSeed is called when you
expect it to be called?
After the call to generateSeed their is also some arithmetic to turn its
byte[] into a long for use by Random's constructor. My missing unit test
is for the process of actually calling generateSeed, converting the
result, and constructing the Random.
Or are you asking how to write tests when you don't know which seed
value your RNGs are using (and therefore can't be certain of the
expected outcomes)?
The easiest solution to that is to not do it. For example, I force both
seeds in my regression tests, so they use the same RNG sequences every
time they run. That works for everything except testing the using of
generateSeed to seed a java.util.Random.
Patricia
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