diff --git a/lib/prism/testing/integration_test.rb b/lib/prism/testing/integration_test.rb
new file mode 100644
index 0000000..9db4d96
--- /dev/null
+++ b/lib/prism/testing/integration_test.rb
@@ -0,0 +1,176 @@
+module Prism
+  module Testing
+    # Mixin for Minitest::Test subclasses that exercises a full request
+    # cycle (router -> middleware -> controller -> view) without a real
+    # socket, the way ActionDispatch::IntegrationTest does in Rails.
+    # Deliberately does NOT require 'minitest' itself: it only calls
+    # #assert, which the including class already has from
+    # Minitest::Test/Minitest::Assertions.
+    #
+    #   class SignupFlowTest < Minitest::Test
+    #     include Prism::Testing::IntegrationTest
+    #     integration_app MyApp
+    #
+    #     def test_signup_then_authenticated_page
+    #       get '/signup'
+    #       post '/users', params: { user: { email: 'a@b.com', password: 'secret123' } }
+    #       assert_response :redirect
+    #       follow_redirect!
+    #       assert_response :success
+    #     end
+    #   end
+    module IntegrationTest
+      def self.included(base)
+        base.extend(ClassMethods)
+      end
+
+      module ClassMethods
+        def integration_app(app = nil)
+          @integration_app = app unless app.nil?
+          @integration_app || (superclass.respond_to?(:integration_app) ? superclass.integration_app : nil)
+        end
+
+        # Opts this test class into Rails-style "transactional fixtures":
+        # every test method (setup, body, and teardown together) runs
+        # inside one `Orm::Store` transaction that is unconditionally
+        # rolled back once the method finishes, pass or fail, so writes
+        # made by one test never leak into the next - no truncating or
+        # reseeding tables between tests. Defaults to `Prism::Orm.store`;
+        # pass `store:` for a test suite that connects a different one, or
+        # `stores:` (an array) when a single test method writes through more
+        # than one independent `Store` (e.g. the app's main store and a
+        # separate jobs queue store) and both need to unwind together.
+        def use_transactional_tests(store: :default, stores: nil)
+          @transactional_tests_stores = stores ? Array(stores) : [store]
+        end
+
+        def transactional_tests_stores
+          @transactional_tests_stores ||
+            (superclass.respond_to?(:transactional_tests_stores) ? superclass.transactional_tests_stores : nil)
+        end
+
+        def transactional_tests_store
+          transactional_tests_stores&.first
+        end
+      end
+
+      def app
+        self.class.integration_app
+      end
+
+      # Overrides Minitest::Test#run only when `use_transactional_tests`
+      # was declared; otherwise defers straight to `super` so every
+      # existing test class (which never calls it) behaves exactly as
+      # before. `super` inside the innermost block still refers to
+      # Minitest::Test#run - Ruby resolves it from the method's lexical
+      # scope, not the block's, even though that block is handed to
+      # #wrap_transactional_stores and only actually invoked several stack
+      # frames away - so setup/the test method/teardown run exactly once,
+      # nested inside every configured store's transaction.
+      def run
+        configured = self.class.transactional_tests_stores
+        return super unless configured
+
+        stores = configured.map { |s| s == :default ? Prism::Orm.store : s }
+        result = nil
+        wrap_transactional_stores(stores) { result = super }
+        result
+      end
+
+      # Each store gets its OWN `TransactionRegistry`, and that registry's
+      # #within rescues Prism::Orm::Rollback itself rather than re-raising
+      # it - so a single `raise Rollback` deep inside a chain of nested
+      # `store.transaction_with_callbacks` calls only ever unwinds the
+      # INNERMOST store; every store around it would see its block return
+      # normally and commit for real. Naively reusing the single-store
+      # "run the body, then raise Rollback" shape here would roll back only
+      # the last configured store. Instead each recursion level opens its
+      # own store's transaction, recurses to run everything inside it
+      # (ultimately reaching `body` exactly once at the bottom), and THEN
+      # raises its OWN Rollback once that unwinds back to it - so every
+      # store gets an explicit rollback signal at its own nesting level.
+      # First store in the list ends up outermost.
+      def wrap_transactional_stores(stores, &body)
+        return body.call if stores.empty?
+
+        head, *tail = stores
+        head.transaction_with_callbacks do
+          wrap_transactional_stores(tail, &body)
+          raise Prism::Orm::Rollback
+        end
+      end
+      private :wrap_transactional_stores
+
+      def session
+        @prism_integration_session ||= IntegrationSession.new(app)
+      end
+
+      def get(path, params: nil, headers: {}, remote_addr: '127.0.0.1')
+        session.get(path, params: params, headers: headers, remote_addr: remote_addr)
+      end
+
+      def head(path, params: nil, headers: {}, remote_addr: '127.0.0.1')
+        session.head(path, params: params, headers: headers, remote_addr: remote_addr)
+      end
+
+      def post(path, params: nil, headers: {}, remote_addr: '127.0.0.1')
+        session.post(path, params: params, headers: headers, remote_addr: remote_addr)
+      end
+
+      def patch(path, params: nil, headers: {}, remote_addr: '127.0.0.1')
+        session.patch(path, params: params, headers: headers, remote_addr: remote_addr)
+      end
+
+      def put(path, params: nil, headers: {}, remote_addr: '127.0.0.1')
+        session.put(path, params: params, headers: headers, remote_addr: remote_addr)
+      end
+
+      def delete(path, params: nil, headers: {}, remote_addr: '127.0.0.1')
+        session.delete(path, params: params, headers: headers, remote_addr: remote_addr)
+      end
+
+      def follow_redirect!
+        session.follow_redirect!
+      end
+
+      def response
+        session.response
+      end
+
+      def cookies
+        session.cookies
+      end
+
+      def assert_response(expected)
+        actual = response.status
+        assert(response_matches?(expected, actual),
+               "expected response #{expected.inspect}, got #{actual} (body: #{response.body})")
+      end
+
+      def assert_redirected_to(path)
+        assert_response(:redirect)
+        location = response.location
+        assert(location && location.end_with?(path.to_s),
+               "expected redirect to #{path.inspect}, got #{location.inspect}")
+      end
+
+      private
+
+      def response_matches?(expected, actual)
+        case expected
+        when Integer then actual == expected
+        when :success, :ok then (200..299).cover?(actual)
+        when :redirect then (300..399).cover?(actual)
+        when :missing, :not_found then actual == 404
+        when :unprocessable then actual == 422
+        when :forbidden then actual == 403
+        when :unauthorized then actual == 401
+        when :too_many_requests then actual == 429
+        when :client_error then (400..499).cover?(actual)
+        when :server_error then (500..599).cover?(actual)
+        else raise ArgumentError, "unknown expected response: #{expected.inspect}"
+        end
+      end
+    end
+  end
+end