Custom LangChain agent written in JavaScript

This workflow has multiple functionalities. It starts with a manual trigger, "When clicking 'Execute Workflow'", that activates two separate paths. The first path takes a preset string "Tell me a joke" and processes it through a custom Language Learning Model (LLM) chain node. This node interacts with an OpenAI node for query processing. The second path takes another preset string "What year was Einstein born?" and passes it to an "Agent" node. This agent further interacts with a Chat OpenAI node and a custom Wikipedia node to produce the required information. The workflow uses both built-in and custom nodes, and integrates with OpenAI for both paths. It's built for experimenting with langua

Help me set up the n8n workflow "Custom LangChain agent written in JavaScript" (https://n8n.io/workflows/1955). It uses: AI Agent, LangChain Code, OpenAI Chat Model, Code Tool. Import the template JSON into my n8n instance, list every credential I need to create, and walk me through testing it.