Merge pull request rails#39480 from rails/js_html_fallback

Add test for HTML format fallback from JS template

actionview/test/fixtures/test/_js_html_fallback.html.erb

@@ -0,0 +1 @@
+<b>Hello from a HTML partial!</b>

actionview/test/fixtures/test/js_html_fallback.js.erb

@@ -0,0 +1 @@
+document.write("<%= j render(partial: "js_html_fallback").chomp.html_safe %>")

actionview/test/template/render_test.rb

@@ -58,6 +58,11 @@ def test_implicit_format_comes_from_parent_template_cascading
     ] }, rendered_templates)
   end
 
+  def test_explicit_js_format_adds_html_fallback
+    rendered_templates = @controller_view.render(template: "test/js_html_fallback", formats: :js)
+    assert_equal(%Q(document.write("<b>Hello from a HTML partial!<\\/b>")\n), rendered_templates)
+  end
+
   def test_render_without_options
     e = assert_raises(ArgumentError) { @view.render() }
     assert_match(/You invoked render but did not give any of (.+) option\./, e.message)