Test::NoWarnings is throwing a warning.

Which warning is that? Please show an SSCCE that reproduces the issue.

use warnings;
use strict;
use Test::More tests=>2;
use Test::NoWarnings;
use Test::Warn;

sub Foo::get_member_id_by_name { warn "foo than bar" };
my $obj = bless {}, 'Foo';

warning_like ( sub { $obj->get_member_id_by_name('smith'); },
    qr/than/, 'warns when more than one name returned' );

__END__

1..2
ok 1 - warns when more than one name returned
ok 2 - no warnings
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By the way, here's the code I use to test warnings:

sub warns (&) {
    my $sub = shift;
    my @warns;
    { local $SIG{__WARN__} = sub { push @warns, shift }; $sub->() }
    return wantarray ? @warns : scalar @warns;
}

print "<$_>\n" for warns { warn "Hello"; warn "World" }

__END__
<Hello at - line 8.
>
<World at - line 8.
>
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And I've learned it's not a good idea to expect a specific number of warnings, since different versions of Perl may issue different warnings. Just do my @warns = warns {...}; and then grep the array for the warning(s) you do or don't expect.

Update: Typo fix.

My bad. Error was actually coming from another test that I forgot to wrap in a warning_like() test. Thanks for the tip.

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Consider using Test::Warnings which roughly combines the functionality of Test::Warn and Test::NoWarnings, plus fixes a few issues with the latter.

I think your code doesn't work because it contains errors

I suggest adding:

use strict ;
use warnings ;
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I did a small test myself, see results below:

use strict ;
use warnings ;
use Test::More ;
use Test::Warn;
warning_like ( sub { warn "Hello"; }, qr /Hello/, 'Hello warning' ) ;
done_testing() ;
__END__
ok 1 - Hello warning
1..1
[download]

OK, was able to get my solution working by calling the clear warnings with its full name: &Test::NoWarnings::clear_warnings.

However, this does seem convoluted. Perhaps there is a better way?