I also ran into this problem, but the solution I have is completely different from the ones suggested above.
I created my knowledge base and web application bot exclusively using the portal. The problem is the configuration. At the time of writing, Bot Template: Node.js> Question and Answer is not working. I needed to create a new web application bot, and I chose C #> Question and Answer instead.
This solved my problem and allowed me to use the Test in Web Chat feature.
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