The mentioned error is because you didn't export doubler. See Exporter for details. First, make it exportable: 

our %EXPORT_TAGS = ( 'all' => [ qw(
    doubler
) ] );

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Second, import it. A normal script would import it as follows: 

use Integer::Doubler qw( doubler );
  -or-
use Integer::Doubler qw( :all );

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But a test script uses use_ok as follows instead in order to report compile issues in the module more nicely: 

BEGIN {
    use_ok 'Integer::Doubler', qw( doubler );
      -or-
    use_ok 'Integer::Doubler', qw( :all );
}

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Finally, I wanted to mention an issue you haven't encountered yet. Don't print from your tests. Use the functions in Test::More instead. You'll use is almost exclusively, using ok only when is isn't sufficient (since is gives more info on failures).

For example, 

print "2 * 2 =", doubler(2);

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should be 
is( doubler(2), 2*2, 'doubler(2)' );

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(The last argument is a short description of the test.)

Now that you have two tests (use_ok and is), you need to tell that to the test harness. 

use Test::More tests => 2;

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In reply to Re: "nmake test" Error... by ikegami
in thread "nmake test" Error... by biohisham

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