I have been seeking advice on writing test case that work across platforms in Testing for read() failures on different platforms

adrianh gave me a really good solution, but I now have a new problem that puzzles me.

adrianh's idea was to overload CORE::GLOBAL::read(), but I am getting a strange behaviour - instead of returning to my calling code, it croaks directly.

Here's the code in the File.t file 

...
$file = File->new('t/file7.test');

eval {
    # declare as local so default is restored on block exit
    local *CORE::GLOBAL::read = sub (*\$$;$) { return undef };

    # method that calls read()
    # the above causes that to fail, and so should
    # croak with a nice message

    $file->header(); 
};
# expected error message returned by the 
# croak in File::header()
like($@, qr(Error in reading file header)); 
...

[download]

And File::header() looks like this 

package File;
...
sub header {
    my ( $self ) = @_;

    my $seek_rc = $self->{FH}->seek($self->{Header}->{OFFSET}, SEEK_SE
+T );

    if ($seek_rc == 0) {
    croak( 'Cannot seek to absolute file position on opened file handl
+e - ', $! );
    }

    my $length = $self->{FH}->read(my $header, $self->{Header}->{Lengt
+h});

    # check if read() had an error
    croak( "Error in reading file header - $!") # pathological test
      unless defined $length;

    croak( 'Error in reading file header - Mismatch between expected l
+ength (', $self->{Header}->{Length}, ") and returned  length ($length
+) byte count")
      unless $length == $self->{Header}->{_Length};

    $header =~ s/(?:\015+)?\012.*$/\n/;   # remove any garbage at end 
+of header and replace with \n

    return $header;
}
...

[download]

So if the read() returns undef, I expect the croak() message to appear with the $! reason for failure.

Instead, I don't get my croak() message , all I get is $! populated with 'Bad file descriptor'. $@ is empty (that is , $@ eq '').

So why aren't I croak()'ing ?

>perl -v This is perl, v5.8.3 built for i686-linux

use brain;

In reply to Overloaded *CORE:: function not behaving correctly by leriksen

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