diff --git a/.gitignore b/.gitignore
index 290f8a8..695c5d0 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,3 +6,4 @@ tmp/
 .ruby-version
 .byebug_history
 coverage/
+vendor/
diff --git a/opencode-rails.gemspec b/opencode-rails.gemspec
index 2407684..50e8027 100644
--- a/opencode-rails.gemspec
+++ b/opencode-rails.gemspec
@@ -47,6 +47,9 @@ Gem::Specification.new do |spec|
   spec.add_runtime_dependency "activestorage", ">= 7.1", "< 9.0"
   spec.add_runtime_dependency "activesupport", ">= 7.1", "< 9.0"
 
-  spec.add_development_dependency "minitest", "~> 5.20"
+  # minitest 6 removed minitest/mock; Object#stub now ships in the extracted
+  # minitest-mock gem, which the suite uses to stub Net::HTTP, File and Tempfile.
+  spec.add_development_dependency "minitest", "~> 6.0"
+  spec.add_development_dependency "minitest-mock", "~> 5.27"
   spec.add_development_dependency "rake", "~> 13.0"
 end
diff --git a/test/test_helper.rb b/test/test_helper.rb
index 3c769f0..a4b1225 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -4,3 +4,4 @@ $LOAD_PATH.unshift File.expand_path("../lib", __dir__)
 
 require "opencode-rails"
 require "minitest/autorun"
+require "minitest/mock"