Simulator

You can use the Simulator in both Dialogflow ES and Dialogflow CX to test your conversation without incurring any charges.

Here is what the simulator looks like in Dialogflow ES:

And this is what the Simulator looks like in Dialogflow CX:

Given that Dialogflow CX is based on state machines, it provides a lot more information in the Simulator (and you often need all that information to understand what is going on so you can debug your CX agent).