Writing this node reminded me of a testing technique I
occasionally find useful.
Consider the following code:
package DeepThought;
sub new { bless {}, shift };
sub foo {
my $self = shift;
$self->bar(42);
};
sub bar {
my ($self, $n) = @_;
print "$self says the answer is $n\n";
};
I want to test that foo calls bar. I could
check the text output by bar, but that ties my test to the
what bar outputs. Since this can change independently I
want to avoid this.
Solution: use local to redefine bar for the
scope of the test. For example:
use Test::More tests => 2;
isa_ok(my $o = DeepThought->new, 'DeepThought');
{
my $ok;
no warnings;
local *DeepThought::bar = sub { $ok = 1 if $_[1] == 42 };
use warnings;
$o->foo();
ok($ok, 'foo called bar');
};
This technique allows you to mock only part of the class you are testing (hence "Micro Mocking" :-). Occasionally very useful.
You can, of course, use the same method for other classes too. For
example, if you had:
package Foo;
use CGI;
sub new {
my $class = shift;
bless {cgi => CGI->new}, $class;
};
You could check that Foo->new called
CGI->new like this:
use Test::More tests => 1;
{
my $called = 0;
no warnings;
local *CGI::new = sub { $called = 1 };
use warnings;
my $o = Foo->new;
ok($called, 'Foo->new called CGI->new');
};
But, by this point, Test::MockObject is probably a more
sensible choice :-)
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