tests: Callbacks generate a variable number of tests that we must count

Author: terryburton

t/20_display.t

@@ -3,16 +3,20 @@
 use strict;
 use warnings;
 
-use Test::More tests => 39;
+use Test::More;
 BEGIN { use_ok('GSAPI') };
 
 use bytes;
 
+my $num_callbacks=0;
+
 my( $width, $height, $raster, $format );
 sub callback
 {
     my( $name, $handle, $device, @more ) = @_;
 
+    $num_callbacks++;
+
     my $pimage;
     if( @more and 1024 < length $more[-1] ) {
         $pimage = pop @_;
@@ -117,3 +121,5 @@ pass( 'run_file' );
 
 GSAPI::exit($gs);
 pass( 'exit' );
+
+done_testing(41 + $num_callbacks);