Re: How to unit test random seeds?
Patricia Shanahan wrote:
Daniel Dyer wrote:
....
Obviously I am unfamiliar with the structure of your code, but the
only thing that comes to mind is to introduce another layer of
indirection. For the RNGs in my Uncommons Maths library, I have a
SeedGenerator strategy interface. This allows me to use seed data
from various sources (/dev/random and random.org, as well as
SecureRandom). If you had a similar arrangement you would be able to
substitute your true seed generator with a mock that returned a known
value, purely for the purpose of testing your arithmetic. You'd have
to decide whether the added complexity is worth it to get the test
coverage that you are looking for.
Interesting. That would solve my unit test problem. As you say, there is
a tradeoff between test coverage and layers of indirection.
I thought some more about this, and it can be made very unobtrusive as a
test feature.
I defined a SeedGenerator interface inside my seed-processing class. It
also has a static anonymous inner class object that implements
SeedGenerator using SecureRandom. The seed-processing class has two
constructors, the normal one that defaults to its own SecureRandom
generator, and a package-scope one for testing that allows the caller to
specify the SeedGenerator. I made the interface extremely simple to code
using SecureRandom.
That makes the seed generator selection invisible for normal uses of the
class, but lets its unit test control the seeds completely.
Patricia
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