Test::MockRandom(3) Replaces random number generation with non-random number generation

VERSION

version 1.01

SYNOPSIS


# 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

This perhaps ridiculous-seeming module was created to test routines that manipulate random numbers by providing a known output from "rand". Given a list of seeds with "srand", it will return each in turn. After seeded random numbers are exhausted, it will always return 0. Seed numbers must be of a form that meets the expected output from "rand" as called with no arguments --- i.e. they must be between 0 (inclusive) and 1 (exclusive). In order to facilitate generating and testing a nearly-one number, this module exports the function "oneish", which returns a number just fractionally less than one.

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 in order to control the output of "rand". See ``USAGE'' for details.

Alternatively, this module can be used to generate objects, with each object maintaining its own distinct seed array.

USAGE

By default, Test::MockRandom does not export any functions. This still allows object-oriented use by calling "Test::MockRandom->new(@seeds)". In order for Test::MockRandom to be more useful, arguments must be provided during the call to "use".

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". 

  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".

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

new

  $obj = new( LIST OF SEEDS );

Returns a new Test::MockRandom object with the specified list of seeds.

srand

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

If called as a bare function call or package method, sets the seed list for bare/package calls to "rand". If called as an object method, sets the seed list for that object only.

rand

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

If called as a bare or package function, returns the next value from the package seed list. If called as an object method, 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, as limits in floating point precision mean that direct numeric comparisons are not reliable. E.g. 

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

oneish

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

A utility function to return a nearly-one value. Equal to ( 2^32 - 1 ) / 2^32. Useful in "srand" and test functions.

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 called from within a BEGIN block. See ``USAGE'' for details.

Most users will not need this function.

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.

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.

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

AUTHOR

David Golden <[email protected]>

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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