Tests: perl module.

test/perl/input_read_offset/psgi.pl

@@ -0,0 +1,7 @@
+my $app = sub {
+    my ($environ) = @_;
+
+    $environ->{'psgi.input'}->read(my $body, 4, 4);
+
+    return ['200', ['Content-Length' => 4], [$body]];
+};