Recognise a # PREAMBLE directive in a t/lib file

This allows a test file to begin with a common pragma line or other setup code and avoid having to repeat that setup across every individual test block in the file.

Author: leonerd

t/test.pl

@@ -1327,11 +1327,15 @@ sub setup_multiple_progs {
 
  open my $fh, '<', $file or die "Cannot open $file: $!\n" ;
  my $found;
+ my $preamble = "";
  while (<$fh>) {
  if (/^__END__/) {
  $found = $found + 1; # don't use ++
  last;
  }
+ if (/^#\s+PREAMBLE\s+(.*)$/) {
+ $preamble .= "$1\n";
+ }
  }
  # This is an internal error, and should never happen. All bar one of
  # the files had an __END__ marker to signal the end of their preamble,
@@ -1346,6 +1350,12 @@ sub setup_multiple_progs {
  unless $found;
 
  my ($t, @p) = _setup_one_file($fh, $file);
+ if (length $preamble) {
+ # @p consists of ($linenumber, $source) pairs, so we only want
+ # to prepend the preamble to the odd numbered elements.
+ # Additionally, the first two elements are (0, $filename).
+ $_ = $preamble . $_ for @p[ grep { $_ % 2 } 2 .. $#p ];
+ }
  $tests += $t;
  push @prgs, @p;