diff --git a/tool/lib/test/unit/core_assertions.rb b/tool/lib/test/unit/core_assertions.rb
index f3cb32a7e6..1c4a254dd0 100644
--- a/tool/lib/test/unit/core_assertions.rb
+++ b/tool/lib/test/unit/core_assertions.rb
@@ -30,7 +30,8 @@ module Test
         include MiniTest::Assertions
       else
         module MiniTest
-          class Skip; end
+          class Assertion < Exception; end
+          class Skip < Assertion; end
         end
 
         require 'pp'