NAME
Test::MockRandom - Replaces random number generation with non-random
number generation
VERSION
This documentation describes version 1.00.
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.
BUGS
Please report any bugs or feature requests using the CPAN Request
Tracker. Bugs can be submitted through the web interface at
<http://rt.cpan.org/Dist/Display.html?Queue=Test::MockRandom>
When submitting a bug or request, please include a test-file or a patch
to an existing test-file that illustrates the bug or desired feature.
SEE ALSO
* Test::MockObject
* Test::MockModule
AUTHOR
David A. Golden (DAGOLDEN)
COPYRIGHT AND LICENSE
Copyright (c) 2004-2007 by David A. Golden
Licensed under the Apache License, Version 2.0 (the "License"); you may
not use this file except in compliance with the License. You may obtain
a copy of the License at <http://www.apache.org/licenses/LICENSE-2.0>
Files produced as output though the use of this software, shall not be
considered Derivative Works, but shall be considered the original work
of the Licensor.
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.