grip.rb

Then /^the "([^\"]*)" "([^\"]*)" should have a "([^\"]*)" attachment$/ do |meth, mdl, field|
	user = mdl.constantize.send(meth,:order=>"created_at")
	user.image.should be_a_kind_of Grip::Attachment
end

story

		Given I am on create account
		...
		When I attach the file "features/support/assets/test_profile_image.jpg" to "user[image]"
		When I press "Save Changes"
		Then my account should be created
		And the "last" "User" should have a "image" attachment
		...

web_steps.rb

# Adds support for validates_attachment_content_type. Without the mime-type getting
# passed to attach_file() you will get a "Photo file is not one of the allowed file types."
# error message 
When /^(?:|I )attach the file "([^\"]*)" to "([^\"]*)"$/ do |path, field|
  type = path.split(".")[1]

  case type
  when "jpg"
    type = "image/jpg" 
  when "jpeg"
    type = "image/jpeg" 
  when "png"
    type = "image/png" 
  when "gif"
    type = "image/gif"
  end
  
  attach_file(field, path, type)
end