stubbing
----------------
subject = TranscodeResolution.new(content_id: "content_stub_id", source_files: source_files, resolutions: resolutions )
subject.stubs(:analyze_sources).returns(["1280x720", "480x360"])
subject.perform
---------------
class TranscodeResolution
  def initialize(content_id:, source_files:, resolutions: [], preserve_aspect_ratio: 'true')
    @content_id = content_id
    @source_files = source_files
  end

 def perform
    if !@resolutions.empty?
      binding.pry
      existing_resolutions = analyze_sources
    end
  end

  private

  def analyze_sources
    puts "do stuff"
  end
end
-------------


[1] pry(#<TranscodeResolution>)> analyze_sources
=> nil
[2] pry(#<TranscodeResolution>)> analyze_sources
=> ["1280x720", "480x360"]