diff --git a/Gemfile b/Gemfile
index f929e4eb2..a067c55b1 100644
--- a/Gemfile
+++ b/Gemfile
@@ -112,6 +112,7 @@ group :development, :test do
 end
 
 group :test do
+  gem 'test-unit', '~> 3.0' # required for Ruby 2.2+
   gem 'rspec-rails'
   gem 'factory_girl_rails', '~> 4.0'
   gem 'faker'
diff --git a/Gemfile.lock b/Gemfile.lock
index 1db7bf001..37bda782e 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -295,6 +295,7 @@ GEM
     polyamorous (0.5.0)
       activerecord (~> 3.0)
     polyglot (0.3.5)
+    power_assert (0.2.4)
     prawn (2.0.2)
       pdf-core (~> 0.6.0)
       ttfunk (~> 1.4.0)
@@ -442,6 +443,8 @@ GEM
       railties (~> 3.0)
     term-ansicolor (1.3.2)
       tins (~> 1.0)
+    test-unit (3.1.3)
+      power_assert
     therubyracer (0.12.2)
       libv8 (~> 3.16.14.0)
       ref
@@ -560,6 +563,7 @@ DEPENDENCIES
   simplecov
   sqlite3
   strong_parameters
+  test-unit (~> 3.0)
   the_sortable_tree!
   therubyracer
   thin