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Michael G Schwern > Test-Random > Test::Random



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Module Version: 20130427   Source  


Test::Random - Make testing random functions deterministic


    use Test::Random;

    ... test as normal ...


This is a testing module to make testing random things a bit more deterministic.

Controlling randomness

Its main function is to allow you to repeat a failing test in the same way it ran before, even if it contained random elements. Test::Random will output the seed used by the random number generator. You can then use this seed to repeat the last test with exactly the same random elements.

You can control the random seed used by Test::Random by setting the TEST_RANDOM_SEED environment variable. This is handy to make test runs repeatable.

    TEST_RANDOM_SEED=12345 perl -Ilib t/some_test.t

Test::Random will output the seed used at the end of each test run. If the test failed it will be visible to the user (ie. on STDERR) otherwise it will be a TAP comment and only visible if the test is run verbosely.

If having new data every run is too chaotic for you, you can set TEST_RANDOM_SEED to something which will remain fixed during a development session. Perhaps the PID of your shell or your uid or the date (20090704, for example).


When you run a test with Test::Random you will see something like this:

    perl some_test.t

    ok 1
    ok 2
    ok 3
    # TEST_RANDOM_SEED=20891494266

If you wish to repeat the circumstances of that test, with the same randomly generated data, you can run it again with the <TEST_RANDOM_SEED> environment variable set to the given seed.

    TEST_RANDOM_SEED=20891494266 perl some_test.t

    ok 1
    ok 2
    ok 3
    # TEST_RANDOM_SEED=20891494266

See your shell and operating system's documentation for details on how to set environment variables.


If something in your code calls srand() all bets are off.


Test::RandomResults, Test::Sims, Data::Random, Data::Generate

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