Much work.

test/test_helpers/session_test_helper.rb

@@ -0,0 +1,19 @@
+module SessionTestHelper
+  def sign_in_as(user)
+    Current.session = user.sessions.create!
+
+    ActionDispatch::TestRequest.create.cookie_jar.tap do |cookie_jar|
+      cookie_jar.signed[:session_id] = Current.session.id
+      cookies["session_id"] = cookie_jar[:session_id]
+    end
+  end
+
+  def sign_out
+    Current.session&.destroy!
+    cookies.delete("session_id")
+  end
+end
+
+ActiveSupport.on_load(:action_dispatch_integration_test) do
+  include SessionTestHelper
+end