diff --git a/jsonapi-resources.gemspec b/jsonapi-resources.gemspec
index c1401490..1d35f95d 100644
--- a/jsonapi-resources.gemspec
+++ b/jsonapi-resources.gemspec
@@ -21,7 +21,8 @@ Gem::Specification.new do |spec|
 
   spec.add_development_dependency 'bundler', '>= 1.17'
   spec.add_development_dependency 'rake'
-  spec.add_development_dependency 'minitest', '~> 5.10', '!= 5.10.2'
+  spec.add_development_dependency 'minitest', '>= 5.10', '!= 5.10.2', '< 7'
+  spec.add_development_dependency 'minitest-mock'
   spec.add_development_dependency 'minitest-spec-rails'
   spec.add_development_dependency 'simplecov'
   spec.add_development_dependency 'pry'
diff --git a/test/test_helper.rb b/test/test_helper.rb
index 7a1bb952..2ac27ee5 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -532,9 +532,6 @@ class CatResource < JSONAPI::Resource
   jsonapi_resources :people
 end
 
-# Ensure backward compatibility with Minitest 4
-Minitest::Test = MiniTest::Unit::TestCase unless defined?(Minitest::Test)
-
 class Minitest::Test
   include Helpers::Assertions
   include Helpers::ValueMatchers