feat(langchain): add toolEmulator middleware (#9339)

Author: christian-bromann

libs/langchain/src/agents/middleware/index.ts

@@ -46,5 +46,9 @@ export {
   toolRetryMiddleware,
   type ToolRetryMiddlewareConfig,
 } from "./toolRetry.js";
+export {
+  toolEmulatorMiddleware,
+  type ToolEmulatorOptions,
+} from "./toolEmulator.js";
 export { type AgentMiddleware } from "./types.js";
 export { countTokensApproximately } from "./utils.js";

libs/langchain/src/agents/middleware/tests/__mocks__/@langchain/openai.ts

@@ -0,0 +1,27 @@
+import { AIMessage } from "@langchain/core/messages";
+
+export const ChatOpenAI = class MockChatOpenAI {
+  lc_kwargs: Record<string, unknown>;
+
+  constructor(params?: Record<string, unknown>) {
+    this.lc_kwargs = params || {};
+  }
+
+  async invoke() {
+    return new AIMessage({
+      content: "Emulated response for openai",
+    });
+  }
+
+  getName() {
+    return "ChatOpenAI";
+  }
+
+  get _modelType() {
+    return "base_chat_model";
+  }
+
+  get lc_runnable() {
+    return true;
+  }
+};