Test::MockObject - Perl extension for emulating troublesome interfaces

  use Test::MockObject;
  my $mock = Test::MockObject->new();
  $mock->set_true( 'somemethod' );
  ok( $mock->somemethod() );

  $mock->set_true( 'veritas')
           ->set_false( 'ficta' )
           ->set_series( 'amicae', 'Sunny', 'Kylie', 'Bella' );

It's a simple program that doesn't use any other modules, and those are easy to test. More often, testing a program completely means faking up input to another module, trying to coax the right output from something you're not supposed to be testing anyway.

Testing is a lot easier when you can control the entire environment. With Test::MockObject, you can get a lot closer.

Test::MockObject allows you to create objects that conform to particular interfaces with very little code. You don't have to reimplement the behavior, just the input and the output.

Please note that it is possible to write highly detailed unit tests that pass even when your integration tests may fail. Testing the pieces individually does not excuse you from testing the whole thing together. I consider this to be a feature.

In cases where you only need to mock one or two pieces of an existing module, consider Test::MockObject::Extends instead.

None by default. Maybe the Test::Builder accessories, in a future version.

The most important thing a Mock Object can do is to conform sufficiently to an interface. For example, if you're testing something that relies on CGI.pm, you may find it easier to create a mock object that returns controllable results at given times than to fake query string input.

The Basics Creates a new mock object. By default, this is a blessed hash. Pass a reference to bless that reference.

        my $mock_array  = Test::MockObject->new( [] );
        my $mock_scalar = Test::MockObject->new( \( my $scalar ) );
        my $mock_code   = Test::MockObject->new( sub {} );
        my $mock_glob   = Test::MockObject->new( \*GLOB );

Mocking

Your mock object is nearly useless if you don't tell it what it's mocking. This is done by installing methods. You control the output of these mocked methods. In addition, any mocked method is tracked. You can tell not only what was called, but which arguments were passed. Please note that you cannot track non-mocked method calls. They will still be allowed, though Test::MockObject will carp() about them. This is considered a feature, though it may be possible to disable this in the future.

As implied in the example above, it's possible to chain these calls together. Thanks to a suggestion from the fabulous Piers Cawley (CPAN RT #1249), this feature came about in version 0.09. Shorter testing code is nice! Adds a coderef to the object. This allows code to call the named method on the object. For example, this code:

        my $mock = Test::MockObject->new();
        $mock->mock( 'fluorinate', 
                sub { 'impurifying precious bodily fluids' } );
        print $mock->fluorinate;

        $mock->fake_module( 'Regexp::English' );

        my $import;
        $mock->fake_module(
                'Regexp::English',
                import => sub { $import = caller }
        );
        use_ok( 'Regexp::Esperanto' );
        is( $import, 'Regexp::Esperanto',
                'Regexp::Esperanto should use() Regexp::English' );

        $mock->fake_module( 'CGI' );
        $mock->fake_new( 'CGI' );

        use_ok( 'Some::Module' );
        my $s = Some::Module->new();
        is( $s->{_cgi}, $mock,
                'new() should create and store a new CGI object' );

Checking Your Mocks Returns a subroutine reference if this particular mocked object can handle the named method, false otherwise. Returns true if the invocant object mocks a particular class. You must have used CWset_isa() first. Checks to see if something has called a named method on the object. This returns a boolean value. The current implementation does not scale especially well, so use this sparingly if you need to search through hundreds of calls. Clears the internal record of all method calls on the object. It's handy to do this every now and then. Note that this does not affect the mocked methods, only all of the methods called on the object to this point. It's handy to CWclear() methods in between series of tests. That makes it much easier to call CWnext_method() without having to skip over the calls from the last set of tests. Returns the name and argument list of the next mocked method called on an object, in list context. In scalar context, returns only the method name. There are two important things to know about this method. First, it starts at the beginning of the call list. If your code runs like this:

        $mock->set_true( 'foo' );
        $mock->set_true( 'bar' );
        $mock->set_true( 'baz' );

        $mock->foo();
        $mock->bar( 3, 4 );
        $mock->foo( 1, 2 );

        my ($name, $args) = $mock->next_call();
        print "$name (@$args)";

        # prints 'foo'

        $name = $mock->next_call();
        print $name;

        # prints 'bar'

        ($name, $args) = $mock->next_call();
        print "$name (@$args)";

        # prints 'foo 1 2'

        $mock->foo();
        $mock->bar();
        $mock->baz();

        $name = $mock->next_call();
        print $name;

        # prints 'foo'

        $name = $mock->next_call( 2 );
        print $name

        # prints 'baz'

        Some::Function( $mock );
        is( $mock->call_pos(1),  'setup',
                'Function() should first call setup()' );
        is( $mock->call_pos(-1), 'end', 
                '... and last call end()' );

        is( ($mock->call_args(1))[0], $mock,
                '... passing the object to setup()' );
        is( scalar $mock->call_args(-1), 0,
                '... and no args to end()' );

        is( $mock->call_args_pos(1, 1), $mock,
                '... passing the object to setup()');

        is( $mock->call_args_string(1), "$mock initialize",
                '... passing object, initialize as arguments' );

        $mock->foo();
        $mock->called_ok( 'foo' );

Logging

Test::MockObject logs all mocked methods by default. Sometimes you don't want to do this. To prevent logging all calls to a given method, prepend the name of the method with CW- when mocking it.

That is:

        $mock->set_true( '-foo', 'bar' );

will set mock both CWfoo() and CWbar(), causing both to return true. However, the object will log only calls to CWbar(), not CWfoo(). To log CWfoo() again, merely mock it again without the leading CW-:

        $mock->set_true( '-foo' );

CW$mock will log all subsequent calls to CWfoo() again.

Subclassing

There are two methods provided for subclassing: This method determines how to call a method (named as CW$method_name) not available in this class. It also controls logging. You may or may not find it useful, but I certainly take advantage of it for Test::MockObject::Extends. This method tracks the call of the named method and its arguments.

* Add a factory method to avoid namespace collisions (soon)

chromatic, <chromatic at wgz dot org>

Thanks go to Curtis 'Ovid' Poe, as well as ONSITE! Technology, Inc., for finding several bugs and providing several constructive suggestions.

Jay Bonci also found a false positive in CWcalled_ok(). Thanks!

Chris Winters was the first to report I'd accidentally scheduled 0.12 for deletion without uploading a newer version. He also gave useful feedback on Test::MockObject::Extends.

Stevan Little provided the impetus and code for CWset_isa().

perl, Test::Tutorial, Test::More, <http://www.perl.com/pub/a/2001/12/04/testing.html>, and <http://www.perl.com/pub/a/2002/07/10/tmo.html>.

Copyright 2002 - 2005 by chromatic <chromatic at wgz dot org>.

This program is free software; you can use, modify, and redistribute it under the same terms as Perl 5.8.x itself.

See http://www.perl.com/perl/misc/Artistic.html