I think you're approaching it the wrong way. You need to treat it as a black box and control just the inputs -- in this case, rand.

I wrote Test::MockRandom for exactly this kind of testing. Use it to test your boundary conditions on rand, as that's the only thing that will matter to whether you get all 10 digits. It's much better than playing with srand.

PIN length is almost an invariant because it almost doesn't depend on any input data. You're only at risk of a 5 digit pin (or greater) if the maximum rand value happened to give you "10" -- so I would check length at the same time that I check what happens when the random value (before multiplication) is nearly one.

Update: Here's what it would look like to check the boundary conditions:

use Test::MockRandom 'Some::Other::Package';
use Some::Other::Package 'pin'; # exports pin()

# list of values for rand to use
srand( ( (0) x 4, ( oneish() ) x 4 ); # 0,0,0,0,1,1,1,1

is( pin(), '0000', "rand always zero" );
is( pin(), '9999', "rand always almost one");

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-xdg

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In reply to Re: Testing Random Code by xdg
in thread Testing Random Code by Ovid

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