write a test for `#form_data?`

The initial attempt was to remove the method at all in
https://github.com/sergey-alekseev/rails/commit/4926aa68c98673e7be88a2d2b57d72dc490bc71c.

The method overrides Rack's `#form_data?`
https://github.com/rack/rack/blob/6f8808d4201e68e4bd780441b3b7bb3ee6d1f43e/lib/rack/request.rb#L172-L184.
Which may have some incorrect implementation actually. `type.nil?` isn't possible I suppose. I'll check.

2 files changed, 29 insertions, 1 deletions

diff --git a/actionpack/lib/action_dispatch/http/request.rb b/actionpack/lib/action_dispatch/http/request.rb
index 732ee67268..d8419ad804 100644
--- a/actionpack/lib/action_dispatch/http/request.rb
+++ b/actionpack/lib/action_dispatch/http/request.rb
@@ -282,8 +282,16 @@ module ActionDispatch
       end
     end
 
+    # Determine whether the request body contains form-data by checking
+    # the request Content-Type for one of the media-types:
+    # "application/x-www-form-urlencoded" or "multipart/form-data". The
+    # list of form-data media types can be modified through the
+    # +FORM_DATA_MEDIA_TYPES+ array.
+    #
+    # A request body is not assumed to contain form-data when no
+    # Content-Type header is provided and the request_method is POST.
     def form_data?
-      FORM_DATA_MEDIA_TYPES.include?(content_mime_type.to_s)
+      FORM_DATA_MEDIA_TYPES.include?(media_type)
     end
 
     def body_stream #:nodoc:
diff --git a/actionpack/test/dispatch/request_test.rb b/actionpack/test/dispatch/request_test.rb
index f208cfda89..672dbd636c 100644
--- a/actionpack/test/dispatch/request_test.rb
+++ b/actionpack/test/dispatch/request_test.rb
@@ -1172,3 +1172,23 @@ class RequestVariant < BaseRequestTest
     end
   end
 end
+
+class RequestFormData < BaseRequestTest
+  test 'media_type is from the FORM_DATA_MEDIA_TYPES array' do
+    assert stub_request('CONTENT_TYPE' => 'application/x-www-form-urlencoded').form_data?
+    assert stub_request('CONTENT_TYPE' => 'multipart/form-data').form_data?
+  end
+
+  test 'media_type is not from the FORM_DATA_MEDIA_TYPES array' do
+    assert !stub_request('CONTENT_TYPE' => 'application/xml').form_data?
+    assert !stub_request('CONTENT_TYPE' => 'multipart/related').form_data?
+  end
+
+  test 'no Content-Type header is provided and the request_method is POST' do
+    request = stub_request('REQUEST_METHOD' => 'POST')
+
+    assert_equal '', request.media_type
+    assert_equal 'POST', request.request_method
+    assert !request.form_data?
+  end
+end