Add failing spec on utf8 filename with percent character

actionpack/test/dispatch/request/multipart_params_parsing_test.rb

@@ -63,6 +63,17 @@ class MultipartParamsParsingTest < ActionDispatch::IntegrationTest
     assert_equal 'contents', file.read
   end
 
+  test "parses utf8 filename with percent character" do
+    params = parse_multipart('utf8_filename')
+    assert_equal %w(file foo), params.keys.sort
+    assert_equal 'bar', params['foo']
+
+    file = params['file']
+    assert_equal 'ファイル%名.txt', file.original_filename
+    assert_equal "text/plain", file.content_type
+    assert_equal 'contents', file.read
+  end
+
   test "parses boundary problem file" do
     params = parse_multipart('boundary_problem_file')
     assert_equal %w(file foo), params.keys.sort

actionpack/test/fixtures/multipart/utf8_filename

@@ -0,0 +1,10 @@
+--AaB03x
+Content-Disposition: form-data; name="foo"
+
+bar
+--AaB03x
+Content-Disposition: form-data; name="file"; filename="ファイル%名.txt"
+Content-Type: text/plain
+
+contents
+--AaB03x--