refactor(watermark): small text based watermarked to increase document visibility

spec/services/watermark_service_spec.rb

@@ -0,0 +1,23 @@
+RSpec.describe WatermarkService do
+  let(:image) { file_fixture("logo_test_procedure.png") }
+  let(:watermark_service) { WatermarkService.new }
+
+  describe '#process' do
+    it 'returns a tempfile if watermarking succeeds' do
+      Tempfile.create do |output|
+        watermark_service.process(image, output)
+        # output size should always be a little greater than input size
+        expect(output.size).to be_between(image.size, image.size * 1.5)
+      end
+    end
+
+    it 'returns nil if metadata is blank' do
+      allow(watermark_service).to receive(:image_metadata).and_return(nil)
+
+      Tempfile.create do |output|
+        expect(watermark_service.process(image.to_path, output)).to be_nil
+        expect(output.size).to eq(0)
+      end
+    end
+  end
+end