1package Test2::Manual::Tooling::Nesting; 2use strict; 3use warnings; 4 5our $VERSION = '0.000143'; 6 71; 8 9__END__ 10 11=head1 NAME 12 13Test2::Manual::Tooling::Nesting - Tutorial for using other tools within your 14own. 15 16=head1 DESCRIPTION 17 18Sometimes you find yourself writing the same test pattern over and over, in 19such cases you may want to encapsulate the logic in a new test function that 20calls several tools together. This sounds easy enough, but can cause headaches 21if not done correctly. 22 23=head1 NAIVE WAY 24 25Lets say you find yourself writing the same test pattern over and over for multiple objects: 26 27 my $obj1 = $class1->new; 28 is($obj1->foo, 'foo', "got foo"); 29 is($obj1->bar, 'bar', "got bar"); 30 31 my $obj2 = $class1->new; 32 is($obj2->foo, 'foo', "got foo"); 33 is($obj2->bar, 'bar', "got bar"); 34 35 ... 10x more times for classes 2-12 36 37The naive way to do this is to write a C<check_class()> function like this: 38 39 sub check_class { 40 my $class = shift; 41 my $obj = $class->new; 42 is($obj->foo, 'foo', "got foo"); 43 is($obj->bar, 'bar', "got bar"); 44 } 45 46 check_class($class1); 47 check_class($class2); 48 check_class($class3); 49 ... 50 51This will appear to work fine, and you might not notice any problems, 52I<so long as the tests are passing.> 53 54=head2 WHATS WRONG WITH IT? 55 56The problems with the naive approach become obvious if things start to fail. 57The diagnostics that tell you what file and line the failure occurred on will be 58wrong. The failure will be reported to the line I<inside> C<check_class>, not 59to the line where C<check_class()> was called. This is problem because it 60leaves you with no idea which class is failing. 61 62=head2 HOW TO FIX IT 63 64Luckily this is extremely easy to fix. You need to acquire a context object at 65the start of your function, and release it at the end... yes it is that simple. 66 67 use Test2::API qw/context/; 68 69 sub check_class { 70 my $class = shift; 71 72 my $ctx = context(); 73 74 my $obj = $class->new; 75 is($obj->foo, 'foo', "got foo"); 76 is($obj->bar, 'bar', "got bar"); 77 78 $ctx->release; 79 } 80 81See, that was easy. With these 2 additional lines we know have proper file+line 82reporting. The nested tools will find the context we acquired here, and know to 83use it's file and line numbers. 84 85=head3 THE OLD WAY (DO NOT DO THIS ANYMORE) 86 87With L<Test::Builder> there was a global variables called 88C<$Test::Builder::Level> which helped solve this problem: 89 90 sub check_class { 91 my $class = shift; 92 93 local $Test::Builder::Level = $Test::Builder::Level + 1; 94 95 my $obj = $class->new; 96 is($obj->foo, 'foo', "got foo"); 97 is($obj->bar, 'bar', "got bar"); 98 } 99 100This variable worked well enough (and will still work) but was not very 101discoverable. Another problem with this variable is that it becomes cumbersome 102if you have a more deeply nested code structure called the nested tools, you 103might need to count stack frames, and hope they never change due to a third 104party module. The context solution has no such caveats. 105 106=head1 SEE ALSO 107 108L<Test2::Manual> - Primary index of the manual. 109 110=head1 SOURCE 111 112The source code repository for Test2-Manual can be found at 113F<https://github.com/Test-More/Test2-Suite/>. 114 115=head1 MAINTAINERS 116 117=over 4 118 119=item Chad Granum E<lt>exodist@cpan.orgE<gt> 120 121=back 122 123=head1 AUTHORS 124 125=over 4 126 127=item Chad Granum E<lt>exodist@cpan.orgE<gt> 128 129=back 130 131=head1 COPYRIGHT 132 133Copyright 2018 Chad Granum E<lt>exodist@cpan.orgE<gt>. 134 135This program is free software; you can redistribute it and/or 136modify it under the same terms as Perl itself. 137 138See F<http://dev.perl.org/licenses/> 139 140=cut 141