1 files changed, 11 insertions, 0 deletions
diff --git a/mrbgems/mruby-sprintf/test/sprintf.rb b/mrbgems/mruby-sprintf/test/sprintf.rb
index ccbd95d51..178904d60 100644
--- a/mrbgems/mruby-sprintf/test/sprintf.rb
+++ b/mrbgems/mruby-sprintf/test/sprintf.rb
@@ -30,3 +30,14 @@ assert("String#% with invalid chr") do
     end
   end
 end
+
+assert("String#% invalid format") do
+  assert_raise ArgumentError do
+    "%?" % ""
+  end
+end
+
+assert("String#% invalid format shared substring") do
+  fmt = ("x"*30+"%!")[0...-1]
+  assert_equal fmt, sprintf(fmt, "")
+end