if it walks like a duck and talks like a duck, it must be a duck

actionpack/test/dispatch/request/multipart_params_parsing_test.rb

@@ -36,7 +36,6 @@ def teardown
     assert_equal 'bar', params['foo']
 
     file = params['file']
-    assert_kind_of Tempfile, file
     assert_equal 'file.txt', file.original_filename
     assert_equal "text/plain", file.content_type
     assert_equal 'contents', file.read
@@ -49,8 +48,6 @@ def teardown
     file = params['file']
     foo  = params['foo']
 
-    assert_kind_of Tempfile, file
-
     assert_equal 'file.txt', file.original_filename
     assert_equal "text/plain", file.content_type
 
@@ -64,8 +61,6 @@ def teardown
 
     file = params['file']
 
-    assert_kind_of Tempfile, file
-
     assert_equal 'file.txt', file.original_filename
     assert_equal "text/plain", file.content_type
     assert ('a' * 20480) == file.read
@@ -77,13 +72,11 @@ def teardown
     assert_equal 'bar', params['foo']
 
     file = params['file']
-    assert_kind_of Tempfile, file
     assert_equal 'file.csv', file.original_filename
     assert_nil file.content_type
     assert_equal 'contents', file.read
 
     file = params['flowers']
-    assert_kind_of Tempfile, file
     assert_equal 'flowers.jpg', file.original_filename
     assert_equal "image/jpeg", file.content_type
     assert_equal 19512, file.size