2 files changed, 45 insertions, 0 deletions
diff --git a/actionview/test/template/controller_helper_test.rb b/actionview/test/template/controller_helper_test.rb
new file mode 100644
index 0000000000..b5e94ea4f1
--- /dev/null
+++ b/actionview/test/template/controller_helper_test.rb
@@ -0,0 +1,21 @@
+require 'abstract_unit'
+
+class ControllerHelperTest < ActionView::TestCase
+  tests ActionView::Helpers::ControllerHelper
+
+  class SpecializedFormBuilder < ActionView::Helpers::FormBuilder ; end
+
+  def test_assign_controller_sets_default_form_builder
+    @controller = OpenStruct.new(default_form_builder: SpecializedFormBuilder)
+    assign_controller(@controller)
+
+    assert_equal SpecializedFormBuilder, self.default_form_builder
+  end
+
+  def test_assign_controller_skips_default_form_builder
+    @controller = OpenStruct.new
+    assign_controller(@controller)
+
+    assert_nil self.default_form_builder
+  end
+end
diff --git a/actionview/test/template/form_helper_test.rb b/actionview/test/template/form_helper_test.rb
index 5c55b154d3..b8cb5bd746 100644
--- a/actionview/test/template/form_helper_test.rb
+++ b/actionview/test/template/form_helper_test.rb
@@ -3269,6 +3269,30 @@ class FormHelperTest < ActionView::TestCase
     ActionView::Base.default_form_builder = old_default_form_builder
   end
 
+  def test_form_builder_override
+    self.default_form_builder = LabelledFormBuilder
+
+    output_buffer = fields_for(:post, @post) do |f|
+      concat f.text_field(:title)
+    end
+
+    expected = "<label for='title'>Title:</label> <input name='post[title]' type='text' id='post_title' value='Hello World' /><br/>"
+
+    assert_dom_equal expected, output_buffer
+  end
+
+  def test_lazy_loading_form_builder_override
+    self.default_form_builder = "FormHelperTest::LabelledFormBuilder"
+
+    output_buffer = fields_for(:post, @post) do |f|
+      concat f.text_field(:title)
+    end
+
+    expected = "<label for='title'>Title:</label> <input name='post[title]' type='text' id='post_title' value='Hello World' /><br/>"
+
+    assert_dom_equal expected, output_buffer
+  end
+
   def test_fields_for_with_labelled_builder
     output_buffer = fields_for(:post, @post, builder: LabelledFormBuilder) do |f|
       concat f.text_field(:title)