diff --git a/.github/workflows/minitest.yml b/.github/workflows/minitest.yml
index a7c8f71..31114ae 100644
--- a/.github/workflows/minitest.yml
+++ b/.github/workflows/minitest.yml
@@ -2,9 +2,9 @@ name: Minitest
 
 on:
   push:
-    branches: [ master ]
+    branches: [ main ]
   pull_request:
-    branches: [ master ]
+    branches: [ main ]
 
 jobs:
   test:
diff --git a/Gemfile b/Gemfile
index 1004d4c..2523fba 100644
--- a/Gemfile
+++ b/Gemfile
@@ -3,5 +3,11 @@ source 'https://rubygems.org'
 rails_version = ENV['RAILS_VERSION']
 gem 'actionpack', rails_version
 
+# Ruby 3.4+ removed these from stdlib, but older Rails versions need them
+if Gem::Version.new(RUBY_VERSION) >= Gem::Version.new('3.4.0')
+  gem 'mutex_m'
+  gem 'bigdecimal'
+end
+
 # Specify your gem's dependencies in auto-session-timeout.gemspec
 gemspec
diff --git a/test/auto_session_timeout_test.rb b/test/auto_session_timeout_test.rb
index 808a6f4..d60cbdd 100644
--- a/test/auto_session_timeout_test.rb
+++ b/test/auto_session_timeout_test.rb
@@ -32,6 +32,68 @@ def user_session_path
     end
   end
 
+  # Stub for testing session_expired? and signing_in?
+  class StubSession < Hash
+  end
+
+  class StubRequest
+    attr_accessor :env, :original_url
+
+    def initialize(path_info: "/", request_method: "GET", original_url: "http://example.com/")
+      @env = {
+        "PATH_INFO" => path_info,
+        "REQUEST_METHOD" => request_method
+      }
+      @original_url = original_url
+    end
+  end
+
+  class StubControllerWithSession
+    include AutoSessionTimeout
+
+    attr_accessor :session, :request, :session_was_reset
+
+    def initialize
+      @session = StubSession.new
+      @request = StubRequest.new
+      @session_was_reset = false
+    end
+
+    def main_app
+      MainApp.new
+    end
+
+    def user_session_path
+      "/users/sign_in"
+    end
+
+    def reset_session
+      @session_was_reset = true
+      @session.clear
+    end
+  end
+
+  class StubUser
+    attr_accessor :auto_timeout
+
+    def initialize(auto_timeout: nil)
+      @auto_timeout = auto_timeout
+    end
+
+    def respond_to?(method)
+      method.to_sym == :auto_timeout || super
+    end
+  end
+
+  class StubControllerWithCurrentUser < StubControllerWithSession
+    attr_accessor :current_user
+
+    def initialize
+      super
+      @current_user = nil
+    end
+  end
+
   describe "#active_url" do
     it "returns main_app.active_url when available" do
       controller = StubController.new
@@ -56,4 +118,166 @@ def user_session_path
     end
   end
 
+  describe "#session_expired?" do
+    it "returns true when session has expired" do
+      controller = StubControllerWithSession.new
+      controller.session[:auto_session_expires_at] = Time.now - 60
+      assert controller.send(:session_expired?, controller)
+    end
+
+    it "returns false when session has not expired" do
+      controller = StubControllerWithSession.new
+      controller.session[:auto_session_expires_at] = Time.now + 60
+      refute controller.send(:session_expired?, controller)
+    end
+
+    it "returns falsy when no expiration is set" do
+      controller = StubControllerWithSession.new
+      refute controller.send(:session_expired?, controller)
+    end
+  end
+
+  describe "#signing_in?" do
+    it "returns true for POST to sign_in_path" do
+      controller = StubControllerWithSession.new
+      controller.request = StubRequest.new(path_info: "/users/sign_in", request_method: "POST")
+      assert controller.send(:signing_in?, controller)
+    end
+
+    it "returns false for GET to sign_in_path" do
+      controller = StubControllerWithSession.new
+      controller.request = StubRequest.new(path_info: "/users/sign_in", request_method: "GET")
+      refute controller.send(:signing_in?, controller)
+    end
+
+    it "returns false for POST to other paths" do
+      controller = StubControllerWithSession.new
+      controller.request = StubRequest.new(path_info: "/other", request_method: "POST")
+      refute controller.send(:signing_in?, controller)
+    end
+  end
+
+  describe "#handle_session_reset" do
+    it "calls reset_session on the controller" do
+      controller = StubControllerWithSession.new
+      controller.session[:auto_session_expires_at] = Time.now + 60
+      controller.session[:user_id] = 123
+
+      refute controller.session_was_reset
+      controller.send(:handle_session_reset, controller)
+
+      assert controller.session_was_reset
+    end
+  end
+
+  describe "session timeout behavior" do
+    # Helper to simulate the before_action logic
+    def simulate_before_action(controller, seconds = nil)
+      if controller.send(:session_expired?, controller) && !controller.send(:signing_in?, controller)
+        controller.send(:handle_session_reset, controller)
+      else
+        unless controller.request.original_url.start_with?(controller.send(:active_url))
+          current_user = controller.respond_to?(:current_user) ? controller.current_user : nil
+          offset = seconds || (current_user&.respond_to?(:auto_timeout) ? current_user.auto_timeout : nil)
+          controller.session[:auto_session_expires_at] = Time.now + offset if offset && offset > 0
+        end
+      end
+    end
+
+    it "resets session when expired and not signing in" do
+      controller = StubControllerWithSession.new
+      controller.session[:auto_session_expires_at] = Time.now - 60
+      controller.request = StubRequest.new(path_info: "/dashboard", request_method: "GET")
+
+      simulate_before_action(controller)
+
+      assert controller.session_was_reset
+    end
+
+    it "does not reset session when signing in even if expired" do
+      controller = StubControllerWithSession.new
+      controller.session[:auto_session_expires_at] = Time.now - 60
+      controller.request = StubRequest.new(path_info: "/users/sign_in", request_method: "POST")
+
+      simulate_before_action(controller)
+
+      refute controller.session_was_reset
+    end
+
+    it "does not reset session when not expired" do
+      controller = StubControllerWithSession.new
+      controller.session[:auto_session_expires_at] = Time.now + 60
+      controller.request = StubRequest.new(path_info: "/dashboard", request_method: "GET")
+
+      simulate_before_action(controller, 300)
+
+      refute controller.session_was_reset
+    end
+
+    it "sets session expiration time with given seconds" do
+      controller = StubControllerWithSession.new
+      controller.request = StubRequest.new(path_info: "/dashboard", request_method: "GET", original_url: "http://example.com/dashboard")
+
+      before_time = Time.now
+      simulate_before_action(controller, 300)
+      after_time = Time.now
+
+      assert controller.session[:auto_session_expires_at] >= before_time + 300
+      assert controller.session[:auto_session_expires_at] <= after_time + 300
+    end
+
+    it "uses current_user.auto_timeout when available" do
+      controller = StubControllerWithCurrentUser.new
+      controller.current_user = StubUser.new(auto_timeout: 600)
+      controller.request = StubRequest.new(path_info: "/dashboard", request_method: "GET", original_url: "http://example.com/dashboard")
+
+      before_time = Time.now
+      simulate_before_action(controller)
+      after_time = Time.now
+
+      assert controller.session[:auto_session_expires_at] >= before_time + 600
+      assert controller.session[:auto_session_expires_at] <= after_time + 600
+    end
+
+    it "does not update expiration for active_url requests" do
+      controller = StubControllerWithSession.new
+      controller.request = StubRequest.new(
+        path_info: "/active",
+        request_method: "GET",
+        original_url: "http://example.com/active"
+      )
+
+      simulate_before_action(controller, 300)
+
+      assert_nil controller.session[:auto_session_expires_at]
+    end
+
+    it "does not set expiration when seconds is nil and no user timeout" do
+      controller = StubControllerWithSession.new
+      controller.request = StubRequest.new(path_info: "/dashboard", request_method: "GET", original_url: "http://example.com/dashboard")
+
+      simulate_before_action(controller, nil)
+
+      assert_nil controller.session[:auto_session_expires_at]
+    end
+
+    it "does not set expiration when seconds is zero" do
+      controller = StubControllerWithSession.new
+      controller.request = StubRequest.new(path_info: "/dashboard", request_method: "GET", original_url: "http://example.com/dashboard")
+
+      simulate_before_action(controller, 0)
+
+      assert_nil controller.session[:auto_session_expires_at]
+    end
+
+    it "does not set expiration when seconds is negative" do
+      controller = StubControllerWithSession.new
+      controller.request = StubRequest.new(path_info: "/dashboard", request_method: "GET", original_url: "http://example.com/dashboard")
+
+      simulate_before_action(controller, -10)
+
+      assert_nil controller.session[:auto_session_expires_at]
+    end
+  end
+
 end