fix(functions): update and fix functions_billing_stop sample

functions/billing/stop-billing/.eslintrc.json

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+{
+  "parserOptions": {
+    "ecmaVersion": 2020
+  }
+}

functions/billing/stop-billing/index.js

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+// Copyright 2025 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.
+
+// [START functions_billing_stop]
+const {CloudBillingClient} = require('@google-cloud/billing');
+const functions = require('@google-cloud/functions-framework');
+const gcpMetadata = require('gcp-metadata');
+
+const billing = new CloudBillingClient();
+
+let projectId = process.env.GOOGLE_CLOUD_PROJECT;
+
+// TODO(developer): Since stopping billing is a destructive action
+// for your project, first validate a test budget with a dry run enabled.
+const dryRun = true;
+
+functions.cloudEvent('StopBillingCloudEvent', async cloudEvent => {
+  if (projectId === undefined) {
+    try {
+      projectId = await gcpMetadata.project('project-id');
+    } catch (error) {
+      console.error('project-id metadata not found:', error);
+
+      console.error(
+        'Project ID could not be found in environment variables ' +
+          'or Cloud Run metadata server. Stopping execution.'
+      );
+      return;
+    }
+  }
+
+  const projectName = `projects/${projectId}`;
+
+  // Find more information about the notification format here:
+  // https://cloud.google.com/billing/docs/how-to/budgets-programmatic-notifications#notification-format
+  const messageData = cloudEvent.data?.message?.data;
+  if (!messageData) {
+    console.error('Invalid CloudEvent: missing data.message.data');
+    return;
+  }
+
+  const eventData = Buffer.from(messageData, 'base64').toString();
+
+  let eventObject;
+  try {
+    eventObject = JSON.parse(eventData);
+  } catch (e) {
+    console.error('Error parsing event data:', e);
+    return;
+  }
+
+  console.log(
+    `Project ID: ${projectId} ` +
+      `Current cost: ${eventObject.costAmount} ` +
+      `Budget: ${eventObject.budgetAmount}`
+  );
+
+  if (eventObject.costAmount <= eventObject.budgetAmount) {
+    console.log('No action required. Current cost is within budget.');
+    return;
+  }
+
+  console.log(`Disabling billing for project '${projectName}'...`);
+
+  const billingEnabled = await _isBillingEnabled(projectName);
+  if (billingEnabled) {
+    await _disableBillingForProject(projectName);
+  } else {
+    console.log('Billing is already disabled.');
+  }
+});
+
+/**
+ * Determine whether billing is enabled for a project
+ * @param {string} projectName The name of the project to check
+ * @returns {boolean} Whether the project has billing enabled or not
+ */
+const _isBillingEnabled = async projectName => {
+  try {
+    console.log(`Getting billing info for project '${projectName}'...`);
+    const [res] = await billing.getProjectBillingInfo({name: projectName});
+
+    return res.billingEnabled;
+  } catch (e) {
+    console.error('Error getting billing info:', e);
+    console.error(
+      'Unable to determine if billing is enabled on specified project, ' +
+        'assuming billing is enabled'
+    );
+
+    return true;
+  }
+};
+
+/**
+ * Disable billing for a project by removing its billing account
+ * @param {string} projectName The name of the project to disable billing
+ * @returns {void}
+ */
+const _disableBillingForProject = async projectName => {
+  if (dryRun) {
+    console.log(
+      '** This script would disable billing here, but "dryRun" has been set to true.' +
+        'Change "dryRun" to alter this behaviour.'
+    );
+    return;
+  }
+
+  // Find more information about `projects/updateBillingInfo` API method here:
+  // https://cloud.google.com/billing/docs/reference/rest/v1/projects/updateBillingInfo
+  try {
+    // To disable billing set the `billingAccountName` field to empty
+    const requestBody = {billingAccountName: ''};
+
+    const [response] = await billing.updateProjectBillingInfo({
+      name: projectName,
+      resource: requestBody,
+    });
+
+    console.log(`Billing disabled. Response: ${JSON.stringify(response)}`);
+  } catch (e) {
+    console.error('Failed to disable billing, check permissions.', e);
+  }
+};
+// [END functions_billing_stop]

functions/billing/stop-billing/package.json

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+{
+  "name": "cloud-functions-stop-billing",
+  "private": true,
+  "version": "0.0.1",
+  "description": "Disable billing with a budget notification.",
+  "main": "index.js",
+  "engines": {
+    "node": ">=20.0.0"
+  },
+  "scripts": {
+    "test": "c8 mocha -p -j 2 test/index.test.js --timeout=5000 --exit"
+  },
+  "author": "Google Inc.",
+  "license": "Apache-2.0",
+  "dependencies": {
+    "@google-cloud/billing": "^5.1.0",
+    "@google-cloud/functions-framework": "^4.0.0",
+    "cloudevents": "^10.0.0",
+    "gcp-metadata": "^7.0.1"
+  },
+  "devDependencies": {
+    "c8": "^10.1.3"
+  }
+}

functions/billing/stop-billing/test/index.test.js

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+// Copyright 2025 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.
+
+const assert = require('assert');
+const {CloudEvent} = require('cloudevents');
+const {getFunction} = require('@google-cloud/functions-framework/testing');
+
+require('../index');
+
+const getDataWithinBudget = () => {
+  return {
+    budgetDisplayName: 'BUDGET_NAME',
+    costAmount: 5.0,
+    costIntervalStart: new Date().toISOString(),
+    budgetAmount: 10.0,
+    budgetAmountType: 'SPECIFIED_AMOUNT',
+    currencyCode: 'USD',
+  };
+};
+
+const getDataOverBudget = () => {
+  return {
+    budgetDisplayName: 'BUDGET_NAME',
+    alertThresholdExceeded: 0.9,
+    costAmount: 20.0,
+    costIntervalStart: new Date().toISOString(),
+    budgetAmount: 10.0,
+    budgetAmountType: 'SPECIFIED_AMOUNT',
+    currencyCode: 'USD',
+  };
+};
+
+/**
+ * Get a simulated CloudEvent for a Budget notification.
+ * Find more examples here:
+ * https://cloud.google.com/billing/docs/how-to/budgets-programmatic-notifications
+ * @param {boolean} isOverBudget - Whether or not the budget has been exceeded.
+ * @returns {CloudEvent} The simulated CloudEvent.
+ */
+const getCloudEventOverBudgetAlert = isOverBudget => {
+  let budgetData;
+
+  if (isOverBudget) {
+    budgetData = getDataOverBudget();
+  } else {
+    budgetData = getDataWithinBudget();
+  }
+
+  const jsonString = JSON.stringify(budgetData);
+  const messageBase64 = Buffer.from(jsonString).toString('base64');
+
+  const encodedData = {
+    message: {
+      data: messageBase64,
+    },
+  };
+
+  return new CloudEvent({
+    specversion: '1.0',
+    id: 'my-id',
+    source: '//pubsub.googleapis.com/projects/PROJECT_NAME/topics/TOPIC_NAME',
+    data: encodedData,
+    type: 'google.cloud.pubsub.topic.v1.messagePublished',
+    datacontenttype: 'application/json',
+    time: new Date().toISOString(),
+  });
+};
+
+describe('index.test.js', () => {
+  describe('functions_billing_stop StopBillingCloudEvent', () => {
+    let consoleOutput = '';
+    const originalConsoleLog = console.log;
+    const originalConsoleError = console.error;
+
+    beforeEach(async () => {
+      consoleOutput = '';
+      console.log = message => (consoleOutput += message + '\n');
+      console.error = message => (consoleOutput += 'ERROR: ' + message + '\n');
+    });
+
+    afterEach(() => {
+      console.log = originalConsoleLog;
+      console.error = originalConsoleError;
+    });
+
+    it('should receive a notification within budget', async () => {
+      const StopBillingCloudEvent = getFunction('StopBillingCloudEvent');
+      const isOverBudget = false;
+      await StopBillingCloudEvent(getCloudEventOverBudgetAlert(isOverBudget));
+
+      assert.ok(
+        consoleOutput.includes(
+          'No action required. Current cost is within budget.'
+        )
+      );
+    });
+
+    it('should receive a notification exceeding the budget and simulate stopping billing', async () => {
+      const StopBillingCloudEvent = getFunction('StopBillingCloudEvent');
+      const isOverBudget = true;
+      await StopBillingCloudEvent(getCloudEventOverBudgetAlert(isOverBudget));
+
+      assert.ok(consoleOutput.includes('Getting billing info'));
+      assert.ok(consoleOutput.includes('Disabling billing for project'));
+      assert.ok(
+        consoleOutput.includes('This script would disable billing here')
+      );
+    });
+  });
+});