add test-unit as development dependency

Gemfile.lock

@@ -7,9 +7,12 @@ GEM
   remote: https://rubygems.org/
   specs:
     git (1.3.0)
+    power_assert (0.4.1)
     rake (12.0.0)
     rake-compiler (0.9.9)
       rake
+    test-unit (3.2.3)
+      power_assert
     thoughtbot-shoulda (2.11.1)
     yajl-ruby (1.3.0)
 
@@ -21,6 +24,7 @@ DEPENDENCIES
   git
   rake
   rake-compiler (~> 0.9.0)
+  test-unit
   thoughtbot-shoulda
   yajl-ruby
 

bert.gemspec

@@ -26,4 +26,5 @@ Gem::Specification.new do |s|
     s.add_development_dependency "rake"
     s.add_development_dependency "rake-compiler", "~> 0.9.0"
     s.add_development_dependency "yajl-ruby"
+    s.add_development_dependency "test-unit"
 end