diff --git a/Gemfile b/Gemfile
index 1f66304..f3e4cea 100644
--- a/Gemfile
+++ b/Gemfile
@@ -5,3 +5,4 @@ gemspec
 
 gem "rake", "~> 12.0"
 gem "minitest", "~> 5.0"
+gem "test-unit"