Test::MockRandom(3)

okay bestie, welcome to Test::MockRandom(3) — yes, a User Contributed Perl Documentation page — and it's lowkey a whole vibe for testing randomness without the randomness. 💅

🌸 NAME 🌸

Test::MockRandom — Replaces random number generation with non-random number generation. that's the whole assignment, no cap. ✨

💖 VERSION 💖

version 1.01 🎀

✨ SYNOPSIS ✨

okay so here's the group-chat demo reel, literally exactly how it looks:

# intercept rand in another package
use Test::MockRandom 'Some::Other::Package';
use Some::Other::Package; # exports sub foo { return rand }
srand(0.13);
foo(); # returns 0.13

# using a seed list and "oneish"
srand(0.23, 0.34, oneish() );
foo(); # returns 0.23
foo(); # returns 0.34
foo(); # returns a number just barely less than one
foo(); # returns 0, as the seed array is empty

# object-oriented, for use in the current package
use Test::MockRandom ();
my $nrng = Test::MockRandom->new(0.42, 0.23);
$nrng->rand(); # returns 0.42

🦋 DESCRIPTION 🦋

okay so this module might look perhaps ridiculous-seeming at first glance, but it was created to test routines that manipulate random numbers by feeding them a known output from rand. iconic behavior. 🫶

You give it a list of seeds with srand, and it returns each one in turn. Once those seeded random numbers are exhausted, it always returns 0. periodt. 💀

Seed numbers have to be in the form that matches the expected output from rand when it's called with no arguments — meaning they must be between 0 (inclusive) and 1 (exclusive). So like, 0 is allowed, 1 is not. That's the boundary, bestie. ⭐

And to make generating/testing a nearly-one number easy, this module exports the function oneish, which returns a number just fractionally less than one. she's almost 1 but not quite, and that's the point. 🎀

Depending on how this module is called with use, it will export rand to a specified package (e.g. a class being tested), effectively overriding and intercepting calls in that package to the built-in rand. It can also override rand in the current package or even globally. In all of these cases, it also exports srand and oneish to the current package so you can control the output of rand. See "USAGE" for the details. no cap.

Alternatively, this module can be used to generate objects, with each object maintaining its own distinct seed array. multiple main characters, each with their own seed array, obsessed. 👑

🎀 USAGE 🎀

By default, Test::MockRandom does not export any functions. That still allows object-oriented use by calling Test::MockRandom->new(@seeds). So you can absolutely still do OO, even with no exports. 🦋

In order for Test::MockRandom to be more useful, arguments must be provided during the call to use. that's the move, bestie.

🍓 use Test::MockRandom 'Target::Package' 🍓

The simplest way to intercept rand in another package is to provide the name(s) of the package(s) for interception as arguments in the use statement. This will export rand to the listed packages and will export srand and oneish to the current package to control the behavior of rand. 🎯

You must use Test::MockRandom before you use the target package. This is a typical case for testing a module that uses random numbers:

use Test::More 'no_plan';
use Test::MockRandom 'Some::Package';
BEGIN { use_ok( Some::Package ) }

# assume sub foo { return rand } was imported from Some::Package

srand(0.5)
is( foo(), 0.5, "is foo() 0.5?") # test gives "ok"

If multiple package names are specified, rand will be exported to all of them. 💅

If you wish to export rand to the current package, simply provide "__PACKAGE__" as the parameter for use, or main if importing to a script without a specified package. This can be part of a list provided to use. All of the following idioms work:

use Test::MockRandom qw( main Some::Package ); # Assumes a script
use Test::MockRandom __PACKAGE__, 'Some::Package';

# The following doesn't interpolate __PACKAGE__ as above, but
# Test::MockRandom will still DWIM and handle it correctly

use Test::MockRandom qw( __PACKAGE__ Some::Package );

🧚 use Test::MockRandom %customized 🧚

As an alternative to a package name as an argument to use, Test::MockRandom will also accept a hash reference with a custom set of instructions for how to export functions:

use Test::MockRandom {
   rand   => [ Some::Package, {Another::Package => 'random'} ],
   srand  => { Another::Package => 'seed' },
   oneish => __PACKAGE__
};

The keys of the hash may be any of rand, srand, and oneish. The values of the hash give instructions for where to export the symbol corresponding to the key. These are interpreted as follows, depending on their type: 👀

• String: a package to which Test::MockRandom will export the symbol
• Hash Reference: the key is the package to which Test::MockRandom will export the symbol and the value is the name under which it will be exported
• Array Reference: a list of strings or hash references which will be handled as above

🌈 Test::MockRandom->export_rand_to() 🌈

In order to intercept the built-in rand in another package, Test::MockRandom must export its own rand function to the target package before the target package is compiled, thus overriding calls to the built-in. The simple approach (described above) of providing the target package name in the use Test::MockRandom statement accomplishes this because use is equivalent to a require and import within a BEGIN block. 🎬

To explicitly intercept rand in another package, you can also call export_rand_to, but it must be enclosed in a BEGIN block of its own. The explicit form also support function aliasing just as with the custom approach with use, described above:

use Test::MockRandom;
BEGIN {Test::MockRandom->export_rand_to('AnotherPackage'=>'random')}
use AnotherPackage;

This BEGIN block must not include a use statement for the package to be intercepted, or perl will compile the package to be intercepted before the export_rand_to function has a chance to execute and intercept calls to the built-in rand. This is very important in testing. 🚨

The export_rand_to call must be in a separate BEGIN block from a use or use_ok test, which should be enclosed in a BEGIN block of its own:

use Test::More tests => 1;
use Test::MockRandom;
BEGIN { Test::MockRandom->export_rand_to( 'AnotherPackage' ); }
BEGIN { use_ok( 'AnotherPackage' ); }

Given these cautions, it's probably best to use either the simple or custom approach with use, which does the right thing in most circumstances. Should additional explicit customization be necessary, Test::MockRandom also provides export_srand_to and export_oneish_to. 💖

🌈 Overriding "rand" globally: use Test::MockRandom 'CORE::GLOBAL' 🌈

This is just like intercepting rand in a package, except that you do it globally by overriding the built-in function in CORE::GLOBAL. global main character energy, but for rand. 👑

use Test::MockRandom 'CORE::GLOBAL';

# or

BEGIN { Test::MockRandom->export_rand_to('CORE::GLOBAL') }

You can always access the real, built-in rand by calling it explicitly as CORE::rand. slay.

💀 Intercepting "rand" in a package that also contains a "rand" function 💀

This is tricky as the order in which the symbol table is manipulated will lead to very different results. 😭

This can be done safely (maybe) if the module uses the same rand syntax/prototype as the system call but offers them up as method calls which resolve at run-time instead of compile time. In this case, you will need to do an explicit intercept (as above) but do it after importing the package. I.e.:

use Test::MockRandom 'SomeRandPackage';
use SomeRandPackage;
BEGIN { Test::MockRandom->export_rand_to('SomeRandPackage');

The first line is necessary to get srand and oneish exported to the current package. The second line will define a sub rand in SomeRandPackage, overriding the results of the first line. The third line then re-overrides the rand. You may see warnings about rand being redefined. 🫠

Depending on how your rand is written and used, there is a good likelihood that this isn't going to do what you're expecting, no matter what. If your package that defines rand relies internally upon the system CORE::GLOBAL::rand function, then you may be best off overriding that instead. 💅

✨ FUNCTIONS ✨

Okay bestie, this is the function menu — every callable goodie, explained with no facts left behind. 🫶

🌱 new 🌱

$obj = new( LIST OF SEEDS );

Returns a brand-new Test::MockRandom object with the exact list of seeds you passed in. Slay. 💅

🎀 srand 🎀

srand( LIST OF SEEDS );
$obj->srand( LIST OF SEEDS);

If you call it as a bare function call or as a package method, it sets the seed list for bare/package calls to rand. If you call it as an object method, it sets the seed list for that object only — main character energy, no sharing. 👑

🦋 rand 🦋

$rv = rand();
$rv = $obj->rand();
$rv = rand(3);

If you call it as a bare or package function, it returns the next value from the package seed list. If you call it as an object method, it returns the next value from the object seed list. ✨

If rand is called with a numeric argument, it follows the same behavior as the built-in function — it multiplies the argument with the next value from the seed array, resulting in a random fractional value between 0 and the argument, just like the built-in. If the argument is 0, undef, or non-numeric, it is treated as if the argument is 1.

Using this with an argument in testing may be complicated, because limits in floating point precision mean that direct numeric comparisons are not reliable. For example:

srand(1/3);
rand(3);       # does this return 1.0 or .999999999 etc.

That comment is the whole mood, honestly. 😭

🌸 oneish 🌸

srand( oneish() );
if ( rand() == oneish() ) { print "It's almost one." };

A utility function that returns a nearly-one value. It is equal to ( 2^32 - 1 ) / 2^32. Useful in srand and test functions. So close to one, but not quite — relatable. 💖

🌈 export_rand_to 🌈

Test::MockRandom->export_rand_to( 'Some::Class' );
Test::MockRandom->export_rand_to( 'Some::Class' => 'random' );

This function exports rand into the specified package namespace. It must be called as a class function. If a second argument is provided, it is taken as the symbol name used in the other package as the alias to rand:

use Test::MockRandom;
BEGIN { Test::MockRandom->export_rand_to( 'Some::Class' => 'random' ); }
use Some::Class;
srand (0.5);
print Some::Class::random(); # prints 0.5

It can also be used to explicitly intercept rand after Test::MockRandom has been loaded. The effect of this function is highly dependent on when it is called in the compile cycle and should usually be called from within a BEGIN block. See USAGE for details.

Most users will not need this function. (But if you do, you already know who you are. 💅)

🧚 export_srand_to 🧚

Test::MockRandom->export_srand_to( 'Some::Class' );
Test::MockRandom->export_srand_to( 'Some::Class' => 'seed' );

This function exports srand into the specified package namespace. It must be called as a class function. If a second argument is provided, it is taken as the symbol name to use in the other package as the alias for srand. This function may be useful if another package wraps srand:

# In Some/Class.pm
package Some::Class;
sub seed { srand(shift) }
sub foo  { rand }

# In a script
use Test::MockRandom 'Some::Class';
BEGIN { Test::MockRandom->export_srand_to( 'Some::Class' ); }
use Some::Class;
seed(0.5);
print foo();   # prints "0.5"

The effect of this function is highly dependent on when it is called in the compile cycle and should usually be called from within a BEGIN block. See USAGE for details.

Most users will not need this function. 🎀

🍓 export_oneish_to 🍓

Test::MockRandom->export_oneish_to( 'Some::Class' );
Test::MockRandom->export_oneish_to( 'Some::Class' => 'nearly_one' );

This function exports oneish into the specified package namespace. It must be called as a class function. If a second argument is provided, it is taken as the symbol name to use in the other package as the alias for oneish. Since oneish is usually only used in a test script, this function is likely only necessary to alias oneish to some other name in the current package:

use Test::MockRandom 'Some::Class';
BEGIN { Test::MockRandom->export_oneish_to( __PACKAGE__, "one" ); }
use Some::Class;
seed( one() );
print foo();   # prints a value very close to one

The effect of this function is highly dependent on when it is called in the compile cycle and should usually be called from within a BEGIN block. See USAGE for details.

Most users will not need this function. 🌸

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👀 SEE ALSO 👀

• Test::MockObject
• Test::MockModule

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🛟 SUPPORT 🛟

🐛 Bugs / Feature Requests 🐛

Please report any bugs or feature requests through the issue tracker at https://github.com/dagolden/Test-MockRandom/issues. You will be notified automatically of any progress on your issue. No ghosting, bestie. 💀

💻 Source Code 💻

This is open source software. The code repository is available for public review and contribution under the terms of the license.

https://github.com/dagolden/Test-MockRandom

git clone https://github.com/dagolden/Test-MockRandom.git

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👑 AUTHOR 👑

David Golden <dagolden@cpan.org>

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📜 COPYRIGHT AND LICENSE 📜

This software is Copyright (c) 2014 by David Golden.

This is free software, licensed under:

The Apache License, Version 2.0, January 2004

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That’s the whole page, bestie — footer vibes only: perl v5.42.0, dated 2016-10-08, for Test::MockRandom(3). Byeee! 💖🎀✨