AWS_Stub_get_object.rb

require 'aws-sdk'

source_file = "movie.mp4"
input_root 'example_net/all/content/video'

client = Aws::S3::Client.new(stub_responses: true)
client.stub_responses(:get_object, -> (context) {
  params = context.params
  if ((params[:key] == source_file) && (params[:bucket] == input_root.split('/').first))
    binding.pry
    params[:key]
  else
    nil
  end
})

result = client.get_object(bucket: "example_net", key: "movie.mp4")

https://aws.amazon.com/blogs/developer/advanced-client-stubbing-in-the-aws-sdk-for-ruby-version-3/