Fix a problem with `Rack::Test::UploadedFile`

In Rails, `ActionDispatch::Http::UploadedFile` has an accessor to access
a `Tempfile` object. However, `Rack::Test::UploadedFile` does not
provide that, but provinding the `#path` method instead. To be able to
support both, we have to check for existance for `#tempfile` method,
then fallback to `#path` method.

Fixes #807

lib/paperclip/io_adapters/uploaded_file_adapter.rb

@@ -2,7 +2,12 @@ module Paperclip
   class UploadedFileAdapter
     def initialize(target)
       @target = target
+
+      if @target.respond_to?(:tempfile)
         @tempfile = copy_to_tempfile(@target.tempfile)
+      else
+        @tempfile = copy_to_tempfile(@target)
+      end
     end
 
     def original_filename

test/helper.rb

@@ -13,8 +13,7 @@ require 'active_support'
 require 'active_support/core_ext'
 require 'mime/types'
 require 'pathname'
-
-require 'pathname'
+require 'ostruct'
 
 puts "Testing against version #{ActiveRecord::VERSION::STRING}"
 

test/uploaded_file_adapter_test.rb

@@ -2,6 +2,7 @@ require './test/helper'
 
 class UploadedFileAdapterTest < Test::Unit::TestCase
   context "a new instance" do
+    context "with UploadedFile responding to #tempfile" do
       setup do
         class UploadedFile < OpenStruct; end
         @file = UploadedFile.new(
@@ -39,7 +40,46 @@ class UploadedFileAdapterTest < Test::Unit::TestCase
         assert expected.length > 0
         assert_equal expected, @subject.read
       end
+    end
+
+    context "with UploadFile responding to #path" do
+      setup do
+        class UploadedFile < OpenStruct; end
+        @file = UploadedFile.new(
+          :original_filename => "5k.png",
+          :content_type => "image/png",
+          :head => "",
+          :path => fixture_file("5k.png")
+        )
+        @subject = Paperclip.io_adapters.for(@file)
+      end
 
+      should "get the right filename" do
+        assert_equal "5k.png", @subject.original_filename
       end
 
+      should "get the content type" do
+        assert_equal "image/png", @subject.content_type
+      end
+
+      should "get the file's size" do
+        assert_equal 4456, @subject.size
+      end
+
+      should "return false for a call to nil?" do
+        assert ! @subject.nil?
+      end
+
+      should "generate a MD5 hash of the contents" do
+        expected = Digest::MD5.file(@file.path).to_s
+        assert_equal expected, @subject.fingerprint
+      end
+
+      should "read the contents of the file" do
+        expected = File.new(@file.path).read
+        assert expected.length > 0
+        assert_equal expected, @subject.read
+      end
+    end
+  end
 end