Testing of exception during import

Dirk80 has asked for the wisdom of the Perl Monks concerning the following question:

Let's assume I have a module which needs 3 import parameters.

package My::Test;

use strict;
use warnings;

use Carp;

sub import
{
    my $class = shift;
    croak "Number of import parameters is wrong, stopped " unless @_ =
+= 3;
    # ...
}

1;
[download]

The good case I can check with use_ok. But the bad cases are my problem, e.g. use this class with less than 3 parameters.

use My::Test "Param1", "Param2"; # dies because it are 2 params and no
+t 3 as expected
[download]

I want to test that this exception was thrown and I also want to check its error message for correctness. Usually I use throws_ok for this. But in this case it doesn't work because the use command is at compile time. I have no idea how to test for this exception.

Thanks for your help!

Comment on Testing of exception during import Select or Download Code

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Re: Testing of exception during import by LanX (Saint) on Jul 01, 2022 at 14:53 UTC
`use` is just a require + import in a BEGIN block. Without BEGIN no compile-time. from the docs: It is exactly equivalent to `BEGIN { require Module; Module->import( LIST ); }` except that Module must be a bareword. alternatively you could try to string eval it, IMHO `eval 'use MODULE args'; # run-time` [download] Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l] [select]
Re: Testing of exception during import by Anonymous Monk on Jul 01, 2022 at 14:51 UTC
FWIW, I would either `use My::Test ();` or `require My::Test;`. Both load the module without calling its `import()` method at all. Then call the import method explicitly: use Test::Exception; use My::Test (); lives_ok { My::Test->import( 1, 2, 5 ) }, 'Three parameters'; throws_ok { My::Test->import( 1, 2 ) } m/Number of import parameters is wrong/, 'Two parameters'; ...	[reply] [d/l] [select]
Re: Testing of exception during import by haukex (Archbishop) on Jul 01, 2022 at 18:46 UTC
IMHO testing is one of those places where you can break some of the "rules" like "don't use stringy `eval`" or "don't check the boolean status of `$@` to see if the `eval` failed or not". The following works on your example code: use warnings; use strict; use Test::More tests=>12; ok ! defined eval "use My::Test; 1"; like $@, qr/\bNumber of import parameters is wrong\b/i; ok ! defined eval "use My::Test qw/foo/; 1"; like $@, qr/\bNumber of import parameters is wrong\b/i; ok ! defined eval "use My::Test qw/foo bar/; 1"; like $@, qr/\bNumber of import parameters is wrong\b/i; ok ! defined eval "use My::Test qw/foo bar quz baz/; 1"; like $@, qr/\bNumber of import parameters is wrong\b/i; ok ! defined eval "use My::Test qw/foo bar quz baz blah/; 1"; like $@, qr/\bNumber of import parameters is wrong\b/i; ok defined eval "use My::Test qw/foo bar quz/; 1"; ok !$@; [download]	[reply] [d/l] [select]
Re: Testing of exception during import by kcott (Archbishop) on Jul 02, 2022 at 04:44 UTC
G'day Dirk80, You may already be aware of this, but in case not, I thought I'd point out that your `import` routine will not be called if your module is loaded like this: `use My::Test ();` [download] See the use function, in particular: "... there is a distinction between omitting LIST (`import` called with no arguments) and an explicit empty LIST () (`import` not called)." It's possible that you have an "XY Problem" here. If you provided some information about the specific problem you're trying to solve, we may be able to offer other (better) solutions. — Ken	[reply] [d/l] [select]
Re^2: Testing of exception during import by Dirk80 (Pilgrim) on Jul 05, 2022 at 08:59 UTC
Thank you all for your answers. The problem was that simple. I fully understood your answers and everything works fine. I'm really glad about this great community and that you help me even if I have sometimes beginner questions.	[reply]