Test2:...Nesting(3perl) Perl Programmers Reference GuideTest2:...Nesting(3perl)
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 2018 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/
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