sub function {
    ...
     if ( ... ) {
        warn "Warning message!";
        print "Press ENTER";
        my $dummy = <STDIN>;
    }
    ...
}

use Test::More;
use Test::FailWarnings;
use Capture::Tiny qw( capture_merged );

ok( my $dummy = capture_stdout{ my $d = choose( function( { opt1 => val1 } ) } );
ok( my $dummy = capture_stdout{ my $d = choose( function( { opt2 => val2 } ) } );

done_testing;

use Test::More;
use Test::Fatal;
use Capture::Tiny qw( capture_merged );

$SIG{__WARN__} = sub { die @_ };

is( exception { my $dummy = capture_merged{ function( { opt1 => val1 } ) } }, undef, "{ opt1 => val1 } does not warn" );
is( exception { my $dummy = capture_merged{ function( { opt2 => val2 } ) } }, undef, "{ opt2 => val2 } does not warn" );

done_testing;