NAME

       Test2::Manual::Tooling::Nesting - Tutorial for using other tools within your own.

DESCRIPTION

       Sometimes you find yourself writing the same test pattern over and over, in such cases you
       may want to encapsulate the logic in a new test function that calls several tools
       together. This sounds easy enough, but can cause headaches if not done correctly.

NAIVE WAY

       Lets say you find yourself writing the same test pattern over and over for multiple
       objects:

           my $obj1 = $class1->new;
           is($obj1->foo, 'foo', "got foo");
           is($obj1->bar, 'bar', "got bar");

           my $obj2 = $class1->new;
           is($obj2->foo, 'foo', "got foo");
           is($obj2->bar, 'bar', "got bar");

           ... 10x more times for classes 2-12

       The naive way to do this is to write a "check_class()" function like this:

           sub check_class {
               my $class = shift;
               my $obj = $class->new;
               is($obj->foo, 'foo', "got foo");
               is($obj->bar, 'bar', "got bar");
           }

           check_class($class1);
           check_class($class2);
           check_class($class3);
           ...

       This will appear to work fine, and you might not notice any problems, so long as the tests
       are passing.

   WHATS WRONG WITH IT?
       The problems with the naive approach become obvious if things start to fail.  The
       diagnostics that tell you what file and line the failure occurred on will be wrong. The
       failure will be reported to the line inside "check_class", not to the line where
       "check_class()" was called. This is problem because it leaves you with no idea which class
       is failing.

   HOW TO FIX IT
       Luckily this is extremely easy to fix. You need to acquire a context object at the start
       of your function, and release it at the end... yes it is that simple.

           use Test2::API qw/context/;

           sub check_class {
               my $class = shift;

               my $ctx = context();

               my $obj = $class->new;
               is($obj->foo, 'foo', "got foo");
               is($obj->bar, 'bar', "got bar");

               $ctx->release;
           }

       See, that was easy. With these 2 additional lines we know have proper file+line reporting.
       The nested tools will find the context we acquired here, and know to use it's file and
       line numbers.

       THE OLD WAY (DO NOT DO THIS ANYMORE)

       With Test::Builder there was a global variables called $Test::Builder::Level which helped
       solve this problem:

           sub check_class {
               my $class = shift;

               local $Test::Builder::Level = $Test::Builder::Level + 1;

               my $obj = $class->new;
               is($obj->foo, 'foo', "got foo");
               is($obj->bar, 'bar', "got bar");
           }

       This variable worked well enough (and will still work) but was not very discoverable.
       Another problem with this variable is that it becomes cumbersome if you have a more deeply
       nested code structure called the nested tools, you might need to count stack frames, and
       hope they never change due to a third party module. The context solution has no such
       caveats.

SEE ALSO

       Test2::Manual - Primary index of the manual.

SOURCE

       The source code repository for Test2-Manual can be found at
       https://github.com/Test-More/Test2-Suite/.

MAINTAINERS

       Chad Granum <exodist@cpan.org>

AUTHORS

       Chad Granum <exodist@cpan.org>

COPYRIGHT

       Copyright 2017 Chad Granum <exodist@cpan.org>.

       This program is free software; you can redistribute it and/or modify it under the same
       terms as Perl itself.

       See http://dev.perl.org/licenses/