Make sure session cookie has the correct path for the tenant

ref: https://fizzy.37signals.com/5986089/collections/7/cards/1234

test/test_helpers/session_test_helper.rb

@@ -4,10 +4,13 @@ module SessionTestHelper
   end
 
   def sign_in_as(user)
-    cookies[:session_token] = nil
+    cookies.delete :session_token
     user = users(user) unless user.is_a? User
     put session_launchpad_path, params: { sig: user.signal_user.perishable_signature }
-    assert cookies[:session_token].present?
+
+    cookie = cookies.get_cookie "session_token"
+    assert_not_nil cookie, "Expected session_token cookie to be set after sign in"
+    assert_equal Account.sole.slug, cookie.path, "Expected session_token cookie to be scoped to account slug"
   end
 
   def sign_out