File handles: Use ObjectSpace for counting open files

spec/prawn/images_spec.rb

@@ -56,35 +56,13 @@
   end
 
   it 'closes opened files again after getting Pathname objects' do
-    # lsof version
-    system_has_lsof = system('lsof -v > /dev/null 2>&1')
-    system_has_grep = system('grep --version > /dev/null 2>&1')
-    if system_has_lsof && system_has_grep
-      # linux and macOS will actually run this spec
-      gc_was_disabled = GC.disable # make sure GC doesn't close file
-
-      open_files_before = `lsof -c ruby | grep "#{filename}"`
-      _info = pdf.image(Pathname.new(filename))
-      expect(`lsof -c ruby | grep "#{filename}"`).to eq(open_files_before)
-
-      GC.enable unless gc_was_disabled
-    else
-      # can't test this on every OS
-      expect(system_has_lsof && system_has_grep).to be_falsy
-    end
-  end
+    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
 
-  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 opened files from pathnames' do
-      _info = pdf.image(Pathname.new(filename))
-      expect(File).to have_received(:binread)
-    end
+    expect(open_files_after).to eq(open_files_before)
   end
 
   context 'setting the length of the bytestream' do