diff --git a/actionpack/CHANGELOG b/actionpack/CHANGELOG
index 052d223ec8815f29810e4d1c42f12f98eee815a5..9e604e37a5e90e37f6c769a4cf59749d5c349db9 100644
--- a/actionpack/CHANGELOG
+++ b/actionpack/CHANGELOG
@@ -1,5 +1,10 @@
 *SVN*
 
+* Added easy support for testing file uploads with fixture_file_upload #4105 [turnip@turnipspatch.com]. Example:
+
+    # Looks in Test::Unit::TestCase.fixture_path + '/files/spongebob.png'
+    post :change_avatar, :avatar => fixture_file_upload('/files/spongebob.png', 'image/png')
+
 * Fixed UrlHelper#current_page? to behave even when url-escaped entities are present #3929 [jeremy@planetargon.com]
 
 * Add ability for relative_url_root to be specified via an environment variable RAILS_RELATIVE_URL_ROOT. [isaac@reuben.com, Nicholas Seckar]
diff --git a/actionpack/lib/action_controller/test_process.rb b/actionpack/lib/action_controller/test_process.rb
index 85bcc7372db2aa70efff4bd171a7ecc33817ef27..5e6f4219467f8ee641564e5e3a839bacb5955ea0 100644
--- a/actionpack/lib/action_controller/test_process.rb
+++ b/actionpack/lib/action_controller/test_process.rb
@@ -289,6 +289,40 @@ def close() end
     def delete() @attributes = {} end
   end
   
+  # Essentially generates a modified Tempfile object similar to the object
+  # you'd get from the standard library CGI module in a multipart
+  # request. This means you can use an ActionController::TestUploadedFile
+  # object in the params of a test request in order to simulate
+  # a file upload.
+  #
+  # Usage example, within a functional test:
+  #   post :change_avatar, :avatar => ActionController::TestUploadedFile.new(Test::Unit::TestCase.fixture_path + '/files/spongebob.png', 'image/png')
+  class TestUploadedFile
+    # The filename, *not* including the path, of the "uploaded" file
+    attr_reader :original_filename
+    
+    # The content type of the "uploaded" file
+    attr_reader :content_type
+    
+    def initialize(path, content_type = 'text/plain')
+      raise "file does not exist" unless File.exist?(path)
+      @content_type = content_type
+      @original_filename = path.sub(/^.*#{File::SEPARATOR}([^#{File::SEPARATOR}]+)$/) { $1 }
+      @tempfile = Tempfile.new(@original_filename)
+      FileUtils.copy_file(path, @tempfile.path)
+    end
+    
+    def path #:nodoc:
+      @tempfile.path
+    end
+    
+    alias local_path path
+    
+    def method_missing(method_name, *args, &block) #:nodoc:
+      @tempfile.send(method_name, *args, &block)
+    end
+  end
+  
   module TestProcess
     def self.included(base)
       # execute the request simulating a specific http method and set/volley the response
@@ -393,6 +427,15 @@ def method_missing(selector, *args)
       return @controller.send(selector, *args) if ActionController::Routing::NamedRoutes::Helpers.include?(selector)
       return super
     end
+    
+    # Shortcut for ActionController::TestUploadedFile.new(Test::Unit::TestCase.fixture_path + path, type). Example:
+    #   post :change_avatar, :avatar => fixture_file_upload('/files/spongebob.png', 'image/png')
+    def fixture_file_upload(path, mime_type = nil)
+      ActionController::TestUploadedFile.new(
+        Test::Unit::TestCase.respond_to?(:fixture_path) ? Test::Unit::TestCase + path : path, 
+        mime_type
+      )
+    end
 
     # A helper to make it easier to test different route configurations.
     # This method temporarily replaces ActionController::Routing::Routes
diff --git a/actionpack/test/controller/test_test.rb b/actionpack/test/controller/test_test.rb
index 25c514d5a3bd12f1d814f5c0709928ef96ff8f4c..06a2ce3eb78c5a20711f245f47e69ce753bbebab 100644
--- a/actionpack/test/controller/test_test.rb
+++ b/actionpack/test/controller/test_test.rb
@@ -49,6 +49,10 @@ def test_only_one_param
     def test_remote_addr
       render :text => (request.remote_addr || "not specified")
     end
+    
+    def test_file_upload
+      render :text => params[:file].size
+    end
 
     def rescue_action(e)
       raise e
@@ -366,4 +370,27 @@ def test_header_properly_reset_after_get_request
       end
     end
   end
+  
+  FILES_DIR = File.dirname(__FILE__) + '/../fixtures/multipart'
+  
+  def test_test_uploaded_file
+    filename = 'mona_lisa.jpg'
+    path = "#{FILES_DIR}/#{filename}"
+    content_type = 'image/png'
+    
+    file = ActionController::TestUploadedFile.new(path, content_type)
+    assert_equal filename, file.original_filename
+    assert_equal content_type, file.content_type
+    assert_equal file.path, file.local_path
+    assert_equal File.read(path), file.read
+  end
+  
+  def test_fixture_file_upload
+    post :test_file_upload, :file => fixture_file_upload(FILES_DIR + "/mona_lisa.jpg", "image/jpg")
+    assert_equal 159528, @response.body
+  end
+  
+  def test_test_uploaded_file_exception_when_file_doesnt_exist
+    assert_raise(RuntimeError) { ActionController::TestUploadedFile.new('non_existent_file') }
+  end
 end
diff --git a/actionpack/test/fixtures/multipart/mona_lisa.jpg b/actionpack/test/fixtures/multipart/mona_lisa.jpg
new file mode 100644
index 0000000000000000000000000000000000000000..5cf3bef3d03b6ad0c49615447b4fcf32aace32f7
Binary files /dev/null and b/actionpack/test/fixtures/multipart/mona_lisa.jpg differ