diff --git a/Gemfile b/Gemfile
index 6f6a625..a08f2c6 100644
--- a/Gemfile
+++ b/Gemfile
@@ -16,5 +16,5 @@ gem "minitest", "~> 5.0"
 gem "mocha"
 
 group :development do
-  gem "rubocop", "~> 1.28.2" # Ruby 2.5 support
+  gem "rubocop", "~> 1.50.2" # Ruby 2.6 support
 end
diff --git a/test/load_path_cache/change_observer_test.rb b/test/load_path_cache/change_observer_test.rb
index 108f0b5..19ff35c 100644
--- a/test/load_path_cache/change_observer_test.rb
+++ b/test/load_path_cache/change_observer_test.rb
@@ -29,7 +29,7 @@ def test_observes_changes
         @arr.unshift("f", "g")
 
         @observer.expects(:push_paths).with(@arr, "h", "i")
-        @arr.concat(%w(h i))
+        @arr.push("h", "i")
 
         @observer.expects(:unshift_paths).with(@arr, "j", "k")
         @arr.prepend("j", "k")
@@ -46,7 +46,7 @@ def test_unregister
         @arr.push("b", "c")
         @arr.append("d", "e")
         @arr.unshift("f", "g")
-        @arr.concat(%w(h i))
+        @arr.push("h", "i")
         @arr.prepend("j", "k")
         @arr.delete(3)
         @arr.compact!