Add AC::TestSession#dig method like AD::Request::Session

actionpack/lib/action_controller/test_case.rb

@@ -202,6 +202,11 @@ def destroy
       clear
     end
 
+    def dig(*keys)
+      keys = keys.map.with_index { |key, i| i.zero? ? key.to_s : key }
+      @data.dig(*keys)
+    end
+
     def fetch(key, *args, &block)
       @data.fetch(key.to_s, *args, &block)
     end

actionpack/test/dispatch/session/test_session_test.rb

@@ -43,6 +43,12 @@ def test_keys_and_values
     assert_equal %w(1 2), session.values
   end
 
+  def test_dig
+    session = ActionController::TestSession.new(one: { two: { three: "3" } })
+    assert_equal("3", session.dig(:one, :two, :three))
+    assert_nil(session.dig(:ruby, :on, :rails))
+  end
+
   def test_fetch_returns_default
     session = ActionController::TestSession.new(one: "1")
     assert_equal("2", session.fetch(:two, "2"))