add initial testing

agent/nodes/model.ts

@@ -0,0 +1,21 @@
+import { task, entrypoint } from "@langchain/langgraph";
+import { BaseMessage, SystemMessage } from "@langchain/core/messages";
+import { ChatOpenAI } from "@langchain/openai"
+import { arithmeticTools } from "../tools/arithmetic";
+
+const model = new ChatOpenAI({
+  model: "gpt-5-mini"
+});
+
+const modelWithTools = model.bindTools(arithmeticTools);
+
+export const modelNode = task({ name: "callLlm" }, async (messages: BaseMessage[]) => {
+    
+
+    return modelWithTools.invoke([
+    new SystemMessage(
+      "You are a helpful assistant tasked with performing arithmetic on a set of inputs."
+    ),
+    ...messages,
+  ]);
+});