I noticed that my rspec tests which interacted with Dragonfly attachments on my models were slowing down my test suite. Without even profiling I could see in my terminal menu bar that running these specs was resulting in system calls to ImageMagick convert and identify commands.

This seemed entirely unnecessary to me in a test environment, so I came up with this small monkeypatch to bypass Dragonfly's typical calls out to ImageMagick:

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module Dragonfly
  module ImageMagick
    module Utils

      private

      # does not run actual ImageMagick conversion, just returns the same temp object
      def convert(temp_object=nil, *_)
        temp_object
      end

      def identify(*_)
        # this is totally arbitrary
        { format: :png, width: 300, height: 250, depth: 8 }
      end
    end
  end
end

YMMV, but this resulted in a pretty significant speed increase in my image-centric application - on the order of 2x faster! Good times.