1Test2::Manual::Tooling:U:sNeerstCionngt(r3i)buted Perl DToecsutm2e:n:tMaatniuoanl::Tooling::Nesting(3)
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NAME

6       Test2::Manual::Tooling::Nesting - Tutorial for using other tools within
7       your own.
8

DESCRIPTION

10       Sometimes you find yourself writing the same test pattern over and
11       over, in such cases you may want to encapsulate the logic in a new test
12       function that calls several tools together. This sounds easy enough,
13       but can cause headaches if not done correctly.
14

NAIVE WAY

16       Lets say you find yourself writing the same test pattern over and over
17       for multiple objects:
18
19           my $obj1 = $class1->new;
20           is($obj1->foo, 'foo', "got foo");
21           is($obj1->bar, 'bar', "got bar");
22
23           my $obj2 = $class1->new;
24           is($obj2->foo, 'foo', "got foo");
25           is($obj2->bar, 'bar', "got bar");
26
27           ... 10x more times for classes 2-12
28
29       The naive way to do this is to write a "check_class()" function like
30       this:
31
32           sub check_class {
33               my $class = shift;
34               my $obj = $class->new;
35               is($obj->foo, 'foo', "got foo");
36               is($obj->bar, 'bar', "got bar");
37           }
38
39           check_class($class1);
40           check_class($class2);
41           check_class($class3);
42           ...
43
44       This will appear to work fine, and you might not notice any problems,
45       so long as the tests are passing.
46
47   WHATS WRONG WITH IT?
48       The problems with the naive approach become obvious if things start to
49       fail.  The diagnostics that tell you what file and line the failure
50       occurred on will be wrong. The failure will be reported to the line
51       inside "check_class", not to the line where "check_class()" was called.
52       This is problem because it leaves you with no idea which class is
53       failing.
54
55   HOW TO FIX IT
56       Luckily this is extremely easy to fix. You need to acquire a context
57       object at the start of your function, and release it at the end... yes
58       it is that simple.
59
60           use Test2::API qw/context/;
61
62           sub check_class {
63               my $class = shift;
64
65               my $ctx = context();
66
67               my $obj = $class->new;
68               is($obj->foo, 'foo', "got foo");
69               is($obj->bar, 'bar', "got bar");
70
71               $ctx->release;
72           }
73
74       See, that was easy. With these 2 additional lines we know have proper
75       file+line reporting. The nested tools will find the context we acquired
76       here, and know to use it's file and line numbers.
77
78       THE OLD WAY (DO NOT DO THIS ANYMORE)
79
80       With Test::Builder there was a global variables called
81       $Test::Builder::Level which helped solve this problem:
82
83           sub check_class {
84               my $class = shift;
85
86               local $Test::Builder::Level = $Test::Builder::Level + 1;
87
88               my $obj = $class->new;
89               is($obj->foo, 'foo', "got foo");
90               is($obj->bar, 'bar', "got bar");
91           }
92
93       This variable worked well enough (and will still work) but was not very
94       discoverable. Another problem with this variable is that it becomes
95       cumbersome if you have a more deeply nested code structure called the
96       nested tools, you might need to count stack frames, and hope they never
97       change due to a third party module. The context solution has no such
98       caveats.
99

SEE ALSO

101       Test2::Manual - Primary index of the manual.
102

SOURCE

104       The source code repository for Test2-Manual can be found at
105       https://github.com/Test-More/Test2-Suite/.
106

MAINTAINERS

108       Chad Granum <exodist@cpan.org>
109

AUTHORS

111       Chad Granum <exodist@cpan.org>
112

114       Copyright 2018 Chad Granum <exodist@cpan.org>.
115
116       This program is free software; you can redistribute it and/or modify it
117       under the same terms as Perl itself.
118
119       See http://dev.perl.org/licenses/
120
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123perl v5.30.0                      2019-07-26Test2::Manual::Tooling::Nesting(3)
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