Add test.

Author: ioquatix

test/rdoc/test_rdoc_markup_heading.rb

@@ -26,4 +26,9 @@ def test_plain_html
     assert_equal 'Hello <strong>Friend</strong>!', @h.plain_html
   end
 
+  def test_plain_html_using_image_alt_as_text
+    h = RDoc::Markup::Heading.new 1, 'rdoc-image:foo.png:Hello World'
+
+    assert_equal 'Hello World', h.plain_html
+  end
 end