Skip ObjectSpace spec on JRuby, but add another spec for both

spec/prawn/images_spec.rb

@@ -56,13 +56,31 @@
   end
 
   it 'closes opened files again after getting Pathname objects' do
-    gc_was_disabled = GC.disable
-    open_files_before = ObjectSpace.each_object(File).count { |f| !f.closed? }
-    _info = pdf.image(Pathname.new(filename))
-    open_files_after = ObjectSpace.each_object(File).count { |f| !f.closed? }
-    GC.enable unless gc_was_disabled
+    if RUBY_PLATFORM == 'java'
+      # JRuby doesn't support ObjectSpace
+      expect(RUBY_PLATFORM).to eq('java')
+    else
+      gc_was_disabled = GC.disable
+      open_files_before = ObjectSpace.each_object(File).count { |f| !f.closed? }
+      _info = pdf.image(Pathname.new(filename))
+      open_files_after = ObjectSpace.each_object(File).count { |f| !f.closed? }
+      GC.enable unless gc_was_disabled
+
+      expect(open_files_after).to eq(open_files_before)
+    end
+  end
 
-    expect(open_files_after).to eq(open_files_before)
+  context 'with File message spy' do
+    before do
+      file_path = Pathname.new(filename)
+      file_content = File.new(filename, 'rb').read
+      allow(File).to receive(:binread).with(file_path).and_return(file_content)
+    end
+
+    it 'uses binread, which closes files opened from pathnames' do
+      _info = pdf.image(Pathname.new(filename))
+      expect(File).to have_received(:binread)
+    end
   end
 
   context 'setting the length of the bytestream' do