fakeModel

const model = fakeModel()
  .respondWithTools([{ name: "search", args: { query: "weather" } }])
  .respond(new AIMessage("Sunny and warm."));

const r1 = await model.invoke([new HumanMessage("What's the weather?")]);
// r1.tool_calls[0].name === "search"

const r2 = await model.invoke([new HumanMessage("Thanks")]);
// r2.content === "Sunny and warm."