Here are some examples on how to test for error messages using CPAN modules.

Check that code does or does not die (with a specific error message):

use Test::Exception;

dies_ok { testsub("die") } "Dies on inappropriate input";
throws_ok { testsub("die screaming") } qr/arrrgh/, "Dies with appropri
+ate error message";
lives_ok { testsub("survive") } "Survives with appropriate input";
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Check that a warning is or is not given:

use Test::Warn;

warning_is { testsub("complain") } qr/nag/, "Gives a specific warning"
+;
warning_is { testsub("quiet") undef, "No warnings given";
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Check that none of the tests you run emit a warning:

use Test::NoWarnings;
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For this last one you'll have to add 1 to the number of tests you run (in your Test::More plan), which will then pass whether any of the tests in this file emitted a warning.

See the perldoc for each of these modules for further examples and documentation.

If you don't want to install Test::Exception (or don't want to rely on it), you can do the same kind of thing manually without too much trouble.

use English '-no_match_vars';

eval { possible_exception_thrower() };
ok( ! $EVAL_ERROR, 'possible_exception_thrower() threw nothing' );

eval { this_should_die() };
ok( $EVAL_ERROR, 'this_should_die() did die' );
like( $EVAL_ERROR, qr/exceptional error text/,
      'this_should_die() died for the expected reason );
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You can use the __WARN__ "signal handler" to check if your code warns the way you want.

{
    my $warning;
    local $SIG{__WARN__} = sub { $warning = shift };

    is( $warning, undef, 'no warnings recorded' );
    code_that_warns();
    is( $warning, 'expected warning',
        'code_that_warns() does indeed warn' );

    $warning = undef;
    non_warning_code();
    is( $warning, undef, 'non_warning_code() is clean' );
}
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If you're going to be pitching (and testing for) more than one warning, then the warning handler should push into an array that you can test against.

There is Test::Exception. It might be what you are looking for

Update: also found Test::Trap and Test::Warn.