use Test::MockRandom 'Target::Package'

  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

  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()

  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'

  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

  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.

"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.

Bugs / Feature Requests

Source Code

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

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