Re: Testing failures: How to override print to make it fail?

[blokhead]

You can force print to fail by selecting a filehandle that you know is unwritable. Here's a quick-n-dirty little module that returns a tied filehandle that fails when written to:

package NoPrint;
use Symbol;

sub new {
    my $sym = gensym;
    tie *$sym, $_[0];
    bless $sym, $_[0];
}
sub TIEHANDLE { bless {}, $_[0] }
sub PRINT { return undef }
sub PRINTF { return undef }
sub WRITE { return undef }

You can now use it like this:

my $old_fh = select NoPrint->new;

## deep inside some test somewhere...
print "foo\n" or warn "print failed (1)";

select $old_fh;

## now printing is back to normal again:
print "foo\n" or warn "print failed (2)";

Update: An alternative that might even be is much cleaner is to localize *STDOUT:

{
    local *STDOUT = NoPrint->new;
    print "foo\n" or warn "print failed (1)";
}

print "foo\n" or warn "print failed (2)";