diff --git a/shims/rubygem/Gemfile b/shims/rubygem/Gemfile
index d5c0f4f9..838eb874 100644
--- a/shims/rubygem/Gemfile
+++ b/shims/rubygem/Gemfile
@@ -5,5 +5,6 @@ source "https://rubygems.org"
 gemspec
 
 group :test do
-  gem "minitest", "~> 5.0"
+  gem "minitest", "~> 6.0"
+  gem "minitest-mock", "~> 5.0"
 end
diff --git a/shims/rubygem/test/test_shim.rb b/shims/rubygem/test/test_shim.rb
index 78fd7558..5dc338cd 100644
--- a/shims/rubygem/test/test_shim.rb
+++ b/shims/rubygem/test/test_shim.rb
@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require "minitest/autorun"
+require "minitest/mock"
 require "digest/sha2"
 
 # Ensure the gem's lib/ is on the load path regardless of working directory.