Add description to a timestamp assertion

Author: aycabta

test/test_rdoc_generator_json_index.rb

@@ -109,7 +109,11 @@ def test_generate
     assert orig_file.mtime.inspect == generated_file.mtime.inspect,
       '.js files should be tha same timestamp of original'
 
-    assert generated_file.mtime < now, '.js files should be the same timestamp'
+    assert generated_file.mtime < now,
+      ".js files should be the same timestamp,\n" +
+      "path: #{generated_file.inspect},\n" +
+      "time: #{generated_file.mtime.inspect},\n" +
+      "now : #{now.inspect}"
 
     generated_search_index = Pathname(File.join @tmpdir, 'js/search_index.js')
     assert generated_search_index.mtime > (now - 1), 'search_index.js should be generated timestamp'