add test and doc page

.ci/sample_tests/pre_post_processing/js.integration.cloudbuild.yaml

@@ -0,0 +1,57 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+steps:
+  - name: "${_IMAGE}"
+    id: "js-pre-post-processing-test"
+    entrypoint: "bash"
+    args:
+      - -c
+      - |
+        set -ex
+        chmod +x .ci/sample_tests/run_tests.sh
+        .ci/sample_tests/run_tests.sh
+    env:
+      - "CLOUD_SQL_INSTANCE=${_CLOUD_SQL_INSTANCE}"
+      - "GCP_PROJECT=${_GCP_PROJECT}"
+      - "DATABASE_NAME=${_DATABASE_NAME}"
+      - "DB_USER=${_DB_USER}"
+      - "TARGET_ROOT=${_TARGET_ROOT}"
+      - "TARGET_LANG=${_TARGET_LANG}"
+      - "TABLE_NAME=${_TABLE_NAME}"
+      - "SQL_FILE=${_SQL_FILE}"
+      - "AGENT_FILE_PATTERN=${_AGENT_FILE_PATTERN}"
+    secretEnv: ["TOOLS_YAML_CONTENT", "GOOGLE_API_KEY", "DB_PASSWORD"]
+
+availableSecrets:
+  secretManager:
+    - versionName: projects/${_GCP_PROJECT}/secrets/${_TOOLS_YAML_SECRET}/versions/5
+      env: "TOOLS_YAML_CONTENT"
+    - versionName: projects/${_GCP_PROJECT_NUMBER}/secrets/${_API_KEY_SECRET}/versions/latest
+      env: "GOOGLE_API_KEY"
+    - versionName: projects/${_GCP_PROJECT}/secrets/${_DB_PASS_SECRET}/versions/latest
+      env: "DB_PASSWORD"
+
+timeout: 1200s
+
+substitutions:
+  _TARGET_LANG: "js"
+  _IMAGE: "node:22"
+  _TARGET_ROOT: "docs/en/samples/pre_post_processing/js"
+  _TABLE_NAME: "hotels_js_pre_post_processing"
+  _SQL_FILE: ".ci/sample_tests/setup_hotels.sql"
+  _AGENT_FILE_PATTERN: "agent.js"
+
+options:
+  logging: CLOUD_LOGGING_ONLY

docs/en/samples/pre_post_processing/js.md

@@ -0,0 +1,31 @@
+---
+title: "(JS) Pre and post processing"
+type: docs
+weight: 5
+description: >
+  How to add pre and post processing to your JS toolbox applications.
+---
+
+## Prerequisites
+
+This tutorial assumes that you have set up a basic toolbox application as described in the [local quickstart](../../getting-started/local_quickstart_js).
+
+This guide demonstrates how to implement these patterns in your Toolbox applications.
+
+## Implementation
+
+{{< tabpane persist=header >}}
+{{% tab header="ADK" text=true %}}
+Coming soon.
+{{% /tab %}}
+{{% tab header="Langchain" text=true %}}
+The following example demonstrates how to use `ToolboxClient` with LangChain's middleware to implement pre and post processing for tool calls.
+
+```js
+{{< include "js/langchain/agent.js" >}}
+```
+
+For more information, see the [LangChain Middleware documentation](https://js.langchain.com/docs/introduction/middleware).
+You can also add model-level (`wrap_model`) and agent-level (`before_agent`, `after_agent`) hooks to intercept messages at different stages of the execution loop. See the [LangChain Middleware documentation](https://js.langchain.com/docs/introduction/middleware) for details on these additional hook types.
+{{% /tab %}}
+{{< /tabpane >}}

docs/en/samples/pre_post_processing/js/agent.test.js

@@ -0,0 +1,92 @@
+// Copyright 2026 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import { describe, test, before, after } from "node:test";
+import assert from "node:assert/strict";
+import fs from "fs";
+import path from "path";
+import { fileURLToPath } from "url";
+
+const ORCH_NAME = process.env.ORCH_NAME;
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+const orchDir = path.join(__dirname, ORCH_NAME);
+const agentPath = path.join(orchDir, "agent.js");
+
+const { main: runAgent } = await import(agentPath);
+
+const GOLDEN_FILE_PATH = path.resolve(__dirname, "../golden.txt");
+
+describe(`${ORCH_NAME} Pre/Post Processing Agent`, () => {
+  let capturedOutput = [];
+  let capturedErrors = [];
+  let originalLog;
+  let originalError;
+
+  before(() => {
+    originalLog = console.log;
+    originalError = console.error;
+
+    console.log = (...args) => {
+      const msg = args.map(a => (typeof a === 'object' ? JSON.stringify(a, null, 2) : String(a))).join(' ');
+      capturedOutput.push(msg);
+    };
+    
+    console.error = (...args) => {
+      const msg = args.map(a => (typeof a === 'object' ? JSON.stringify(a, null, 2) : String(a))).join(' ');
+      capturedErrors.push(msg);
+    };
+  });
+
+  after(() => {
+    console.log = originalLog;
+    console.error = originalError;
+  });
+
+  test("runs without errors and outputContainsRequiredKeywords", async () => {
+    capturedOutput = [];
+    capturedErrors = [];
+
+    await runAgent();
+    if (capturedErrors.length > 0) {
+        console.error("Captured Stderr:", capturedErrors.join("\n"));
+    }
+    assert.equal(
+        capturedErrors.length, 
+        0, 
+        `Script produced stderr: ${capturedErrors.join("\n")}`
+    );
+
+    const actualOutput = capturedOutput.join("\n");
+
+    assert.ok(
+      actualOutput.length > 0,
+      "Assertion Failed: Script ran successfully but produced no output."
+    );
+
+    const goldenFile = fs.readFileSync(GOLDEN_FILE_PATH, "utf8");
+    const keywords = goldenFile.split("\n").filter((kw) => kw.trim() !== "");
+    const missingKeywords = [];
+
+    for (const keyword of keywords) {
+      if (!actualOutput.includes(keyword)) {
+        missingKeywords.push(keyword);
+      }
+    }
+
+    assert.ok(
+      missingKeywords.length === 0,
+      `Assertion Failed: The following keywords were missing from the output: [${missingKeywords.join(", ")}]`
+    );
+  });
+});

docs/en/samples/pre_post_processing/js/langchain/agent.js

@@ -159,4 +159,6 @@ async function main() {
 
 if (process.argv[1] === fileURLToPath(import.meta.url)) {
   main();
-}
+}
+
+export { main };