temporary_assign.rb

def temporary_assign(object, attribute, new_value)
  previous_value = object.public_send attribute
  object.public_send "#{attribute}=", new_value
  yield
ensure
  object.public_send "#{attribute}=", previous_value
end

# Example usage:
# Want to debug SQL queries in tests? Log to STDOUT just for the
# queries you want to check and avoid the noise of the test suite
temporary_assign ActiveRecord::Base, :logger, Logger.new(STDOUT) do
  # Some complex AR query
  if user.has_role? :admin
    scope.all
  else
    Agency.with_roles([:manager, :user], user).uniq
  end
end