Sending Production-Ready MMS with Node.js and Plivo - code-examples -

Multimedia Messaging Service (MMS) allows you to enrich your user communication by sending messages that include images, GIFs, videos, and audio, alongside text. While standard Short Message Service (SMS) is limited to text, MMS provides a more engaging and informative experience.

This guide provides a comprehensive, step-by-step walkthrough for building a production-ready Node.js application capable of sending MMS messages using the Plivo communications platform API. We will build a simple API endpoint that accepts recipient details and media information, then reliably sends the MMS via Plivo.

Project Goals:

  • Set up a Node.js project using Express.js.
  • Integrate the Plivo Node.js SDK for sending MMS.
  • Build a secure API endpoint to trigger MMS sending.
  • Implement proper configuration management for API keys and settings.
  • Include input validation, error handling, and basic logging.
  • Provide instructions for testing and verification.
  • Discuss deployment considerations and potential caveats.

Technologies Used:

  • Node.js: A JavaScript runtime environment for server-side development.
  • Express.js: A minimal and flexible Node.js web application framework.
  • Plivo Node.js SDK: Simplifies interaction with the Plivo API.
  • dotenv: Manages environment variables for configuration.
  • express-validator: Middleware for request data validation.
  • Postman / curl: For testing the API endpoint.

Prerequisites:

  • Node.js and npm (or yarn) installed.
  • A Plivo account (a free trial account is sufficient to start).
  • Basic understanding of JavaScript, Node.js, APIs, and terminal commands.
  • A publicly accessible URL for your media file (e.g., hosted on AWS S3, Cloudinary, or even a public Giphy link for testing).

System Architecture:

graph LR
    A[Client / User] -- HTTP POST Request --> B(Node.js / Express API);
    B -- Send MMS Request --> C(Plivo API);
    C -- Delivers MMS --> D(Recipient's Mobile Device);
    B -- API Response (Success/Error) --> A;

    subgraph 'Our Application'
        B
    end

    subgraph 'External Service'
        C
    end

This guide will walk you through creating the ""Node.js / Express API"" component.

1. Setting Up the Project

Let's initialize our Node.js project and install the necessary dependencies.

  1. Create Project Directory: Open your terminal and create a new directory for your project, then navigate into it.

    mkdir node-plivo-mms
cd node-plivo-mms

  2. Initialize Node.js Project: This creates a package.json file to manage dependencies and project information.

    npm init -y

  3. Install Dependencies: We need express for the web server, plivo for the SDK, dotenv for environment variables, and express-validator for input validation.

    npm install express plivo dotenv express-validator
    • express: The web framework.
    • plivo: The official Plivo SDK.
    • dotenv: Loads environment variables from a .env file into process.env. Essential for keeping secrets out of code.
    • express-validator: Provides middleware for validating incoming request data, crucial for security and data integrity.

  4. Set Up Project Structure: Create the following basic structure within your node-plivo-mms directory:

    node-plivo-mms/
├── src/
│   ├── controllers/
│   │   └── mmsController.js
│   ├── middleware/
│   │   └── validators.js
│   ├── routes/
│   │   └── mmsRoutes.js
│   ├── services/
│   │   └── plivoService.js
│   └── app.js
├── .env
├── .gitignore
└── package.json
    • src/: Contains the main application code.
    • controllers/: Handles incoming requests, validates data, and calls services.
    • middleware/: Contains custom middleware, like our validators.
    • routes/: Defines API endpoints and maps them to controllers.
    • services/: Contains business logic, including interaction with external APIs like Plivo.
    • app.js: Sets up the Express application, middleware, and starts the server.
    • .env: Stores sensitive configuration like API keys.
    • .gitignore: Prevents sensitive files (like .env) and unnecessary files (like node_modules) from being committed to version control.

  5. Create .gitignore: Create a file named .gitignore in the project root and add the following:

    # Dependencies
node_modules/

# Environment variables
.env

# Logs
logs
*.log

# OS generated files
.DS_Store
Thumbs.db

  6. Set Up Environment Variables (.env): Create a file named .env in the project root. This file will hold your Plivo credentials and configuration. Never commit this file to Git.

    # Plivo Credentials
PLIVO_AUTH_ID=YOUR_PLIVO_AUTH_ID
PLIVO_AUTH_TOKEN=YOUR_PLIVO_AUTH_TOKEN

# Plivo MMS Enabled Number (must be purchased from Plivo and support MMS)
PLIVO_SOURCE_NUMBER=YOUR_PLIVO_MMS_NUMBER

# Server Configuration
PORT=3000
    • PLIVO_AUTH_ID, PLIVO_AUTH_TOKEN: Your Plivo API credentials.
    • PLIVO_SOURCE_NUMBER: The Plivo phone number (in E.164 format, e.g., +14155551212) that will send the MMS. It must be MMS-enabled.
    • PORT: The port on which your Node.js application will listen.

2. Plivo Account Setup

Before writing code, ensure your Plivo account is ready.

  1. Sign Up/Log In: Go to Plivo.com and sign up for an account or log in.
  2. Find Auth ID and Auth Token:
    • Log in to the Plivo console.
    • Your Auth ID and Auth Token are prominently displayed on the overview dashboard page.
    • Copy these values and paste them into your .env file for PLIVO_AUTH_ID and PLIVO_AUTH_TOKEN.
  3. Get an MMS-Enabled Phone Number:
    • Navigate to ""Phone Numbers"" > ""Buy Numbers"" in the Plivo console.
    • Search for numbers, ensuring you filter by ""MMS"" capability. Plivo currently supports MMS in the US and Canada.
    • Purchase a suitable number.
    • Go to ""Phone Numbers"" > ""Your Numbers"". Verify that the number you purchased has the MMS capability listed.
    • Copy this number (including the leading + and country code) and paste it into your .env file for PLIVO_SOURCE_NUMBER.
  4. Trial Account Limitation (Sandbox Numbers):
    • IMPORTANT: If you are using a Plivo trial account, you can only send messages to phone numbers that have been verified in your account. This is a very common reason for failures when starting out.
    • Navigate to ""Messaging"" > ""Sandbox Numbers"".
    • You MUST add and verify the phone number(s) you intend to use as recipients during testing here. Failure to do so will result in failed messages.

3. Implementing Core MMS Sending Logic (Service)

We'll encapsulate the Plivo interaction within a dedicated service file.

Create src/services/plivoService.js:

// src/services/plivoService.js

const plivo = require('plivo');
require('dotenv').config(); // Ensure environment variables are loaded

// Initialize the Plivo client only once using environment variables
// Note: Client initialization captures env vars at the time of require/load.
// For tests involving changing credentials, ensure modules are reset.
let client;
try {
  client = new plivo.Client(
    process.env.PLIVO_AUTH_ID,
    process.env.PLIVO_AUTH_TOKEN
  );
} catch (error) {
  console.error(""Failed to initialize Plivo client. Check AUTH_ID/AUTH_TOKEN."", error);
  // Depending on application needs, you might want to prevent startup
  // or handle this more gracefully than just logging.
}

/**
 * Sends an MMS message using Plivo.
 * Reads sensitive config directly inside the function for better testability
 * and to reflect potential runtime changes if not using singleton patterns.
 *
 * @param {string} destinationNumber - The recipient's phone number (E.164 format).
 * @param {string} text - The text content of the message.
 * @param {string} mediaUrl - The publicly accessible URL of the media file.
 * @returns {Promise<object&gt;} - A promise that resolves with the Plivo API response.
 * @throws {Error} - Throws an error if sending fails or config is missing.
 */
const sendMms = async (destinationNumber, text, mediaUrl) =&gt; {
  const sourceNumber = process.env.PLIVO_SOURCE_NUMBER;
  const authId = process.env.PLIVO_AUTH_ID;
  const authToken = process.env.PLIVO_AUTH_TOKEN;

  // Check for essential configuration *inside* the function call
  if (!sourceNumber) {
    throw new Error('Plivo source number is not configured in .env');
  }
  if (!authId || !authToken) {
    throw new Error('Plivo Auth ID or Auth Token is missing in .env');
  }
  if (!client) {
      throw new Error('Plivo client is not initialized. Check credentials.');
  }

  // Log initiation attempt (consider replacing with a proper logger in production)
  console.log(`Attempting to send MMS to ${destinationNumber} from ${sourceNumber}`);

  try {
    const response = await client.messages.create(
      sourceNumber,      // src
      destinationNumber, // dst
      text,              // text
      {
        type: 'mms',
        media_urls: [mediaUrl], // Array of media URLs
        // You can also use media_ids if you upload media via the Plivo console:
        // media_ids: ['YOUR_UPLOADED_MEDIA_ID']
      },
      // Optional: Callback URL for delivery status updates
      // {
      //   url: 'YOUR_STATUS_CALLBACK_URL',
      //   method: 'POST'
      // }
    );

    // Log success (consider replacing with a proper logger in production)
    console.log('Plivo API Response:', response);
    return response;
  } catch (error) {
    // Log error (consider replacing with a proper logger in production)
    console.error('Error sending MMS via Plivo:', error);
    // Re-throw the error to be handled by the controller/middleware
    throw error;
  }
};

module.exports = {
  sendMms,
};

Explanation:

  • We import plivo and load environment variables using dotenv.config().
  • The Plivo Client is initialized. Note that it captures PLIVO_AUTH_ID and PLIVO_AUTH_TOKEN at the time it's first loaded.
  • The sendMms function takes the destination number, text, and media URL as arguments.
  • Checks for essential configuration (sourceNumber, PLIVO_AUTH_ID, PLIVO_AUTH_TOKEN) are performed inside the function to make testing environment variable changes easier.
  • client.messages.create is the core Plivo SDK method used.
    • src: Your Plivo MMS number (PLIVO_SOURCE_NUMBER).
    • dst: The recipient's number.
    • text: The message body.
    • The fourth argument is an options object where we specify type: 'mms' and provide the media_urls as an array. Plivo will fetch the media from this URL and attach it.
    • The URL in media_urls must be publicly accessible.
    • An optional fifth argument can provide callback details for status updates (not implemented in this basic guide).
  • We use async/await for cleaner asynchronous code.
  • Note on Logging: console.log and console.error are used here for simplicity. In a production environment, replace these with a robust logging library like Winston or Pino (discussed further in Deployment section).
  • Errors during the API call are caught, logged, and re-thrown for higher-level handling.

4. Building the API Layer (Routes and Controller)

Now, let's create the Express route and controller to expose our MMS sending functionality via an API endpoint.

1. Create Route (src/routes/mmsRoutes.js):

// src/routes/mmsRoutes.js

const express = require('express');
const mmsController = require('../controllers/mmsController');
const { validateSendMms } = require('../middleware/validators'); // We'll create this next

const router = express.Router();

// Define the endpoint: POST /api/mms/send
// It uses validation middleware before hitting the controller
router.post('/send', validateSendMms, mmsController.sendMmsHandler);

module.exports = router;

Explanation:

  • We create an Express router instance.
  • We define a POST route at /send. The full path will be /api/mms/send when mounted in app.js.
  • Crucially, we include validateSendMms middleware (which we'll create next) to validate the request body before the mmsController.sendMmsHandler is executed.
  • The request is then passed to the controller function.

2. Create Controller (src/controllers/mmsController.js):

// src/controllers/mmsController.js

const { validationResult } = require('express-validator');
const plivoService = require('../services/plivoService');

/**
 * Handles the API request to send an MMS.
 * Validates input, calls the Plivo service, and sends the response.
 */
const sendMmsHandler = async (req, res, next) =&gt; {
  // Check for validation errors
  const errors = validationResult(req);
  if (!errors.isEmpty()) {
    // If validation fails, return 400 Bad Request with error details
    return res.status(400).json({ errors: errors.array() });
  }

  // Extract validated data from request body
  const { destinationNumber, text, mediaUrl } = req.body;

  try {
    // Call the service function to send the MMS
    const result = await plivoService.sendMms(destinationNumber, text, mediaUrl);

    // Send success response back to the client
    res.status(200).json({
      message: 'MMS sending initiated successfully.',
      plivoResponse: result,
    });
  } catch (error) {
    // Pass errors to the central error handling middleware (created later)
    next(error);
  }
};

module.exports = {
  sendMmsHandler,
};

Explanation:

  • We import the validationResult function from express-validator and our plivoService.
  • The sendMmsHandler function first checks if validationResult(req) found any errors defined by our validator middleware. If so, it immediately sends a 400 Bad Request response.
  • If validation passes, it extracts the destinationNumber, text, and mediaUrl from the request body (req.body).
  • It calls plivoService.sendMms within a try...catch block.
  • On success, it sends a 200 OK response including the Plivo API's confirmation.
  • If plivoService.sendMms throws an error (either configuration error or Plivo API error), the catch block catches it and passes it to Express's error handling mechanism using next(error).

5. Implementing Input Validation

Validating input is critical for security and preventing errors. We'll use express-validator.

Create the directory src/middleware and inside it, create validators.js:

// src/middleware/validators.js

const { body } = require('express-validator');

const validateSendMms = [
  // Validate destinationNumber: must be a non-empty string, likely in E.164 format
  // Note: Strict E.164 validation can be complex, this is a basic check.
  // Consider using a library like 'google-libphonenumber' for robust validation if needed.
  body('destinationNumber')
    .trim()
    .notEmpty().withMessage('Destination number is required.')
    .isString().withMessage('Destination number must be a string.')
    .matches(/^\+[1-9]\d{1,14}$/).withMessage('Destination number must be in E.164 format (e.g., +14155551212).'),

  // Validate text: must be a non-empty string
  body('text')
    .trim()
    .notEmpty().withMessage('Text message is required.')
    .isString().withMessage('Text must be a string.'),

  // Validate mediaUrl: must be a non-empty string and a valid URL
  body('mediaUrl')
    .trim()
    .notEmpty().withMessage('Media URL is required.')
    .isURL().withMessage('Media URL must be a valid URL.'),
];

module.exports = {
  validateSendMms,
};

Explanation:

  • We use the body function from express-validator to define validation rules for fields expected in the request body.
  • destinationNumber: We check it's not empty, is a string, and roughly matches the E.164 format (starts with +, followed by digits). For production, consider more robust phone number validation.
  • text: Checked for non-emptiness and being a string.
  • mediaUrl: Checked for non-emptiness and being a valid URL format using isURL().
  • .trim() removes leading/trailing whitespace.
  • .withMessage() provides custom error messages.
  • This validateSendMms array of middleware is exported and used in src/routes/mmsRoutes.js.

6. Setting Up the Express App and Error Handling

Now, let's tie everything together in src/app.js.

// src/app.js

const express = require('express');
const dotenv = require('dotenv');
const mmsRoutes = require('./routes/mmsRoutes');

// Load environment variables from .env file
dotenv.config();

// Create Express app instance
const app = express();

// Middleware to parse JSON request bodies
app.use(express.json());
// Middleware to parse URL-encoded request bodies (optional, but common)
app.use(express.urlencoded({ extended: true }));

// --- Routes ---
// Mount the MMS routes under the /api/mms path
app.use('/api/mms', mmsRoutes);

// --- Basic Health Check Route ---
app.get('/health', (req, res) =&gt; {
  res.status(200).json({ status: 'UP', timestamp: new Date().toISOString() });
});

// --- Central Error Handling Middleware ---
// This middleware catches errors passed via next(error)
// IMPORTANT: It must be defined *after* all other app.use() and routes calls
app.use((err, req, res, next) =&gt; {
  // Use a proper logger in production instead of console.error
  console.error('Unhandled Error:', err);

  // Determine status code: use error's status or default to 500
  const statusCode = err.status || err.statusCode || 500;

  // Send a generic error response
  // Avoid sending detailed internal error messages in production
  res.status(statusCode).json({
    message: 'An unexpected error occurred.',
    // Optionally include error details in development only
    error: process.env.NODE_ENV === 'development' ? err.message : undefined,
  });
});

// --- Start the Server ---
const PORT = process.env.PORT || 3000;

app.listen(PORT, () =&gt; {
  // Use a proper logger in production
  console.log(`Server running on port ${PORT}`);
  // Verify essential config on startup
  if (!process.env.PLIVO_AUTH_ID || !process.env.PLIVO_AUTH_TOKEN) {
      console.warn('WARNING: Plivo Auth ID or Token is missing in .env! Client may not initialize.');
  }
  if (!process.env.PLIVO_SOURCE_NUMBER) {
      console.warn('WARNING: Plivo source number is missing in .env! MMS sending will fail.');
  } else {
      console.log(`Configured to send MMS from: ${process.env.PLIVO_SOURCE_NUMBER}`);
  }
});

module.exports = app; // Export for potential testing

Explanation:

  • Load dotenv first to ensure environment variables are available.
  • Create the express app.
  • express.json(): Essential middleware to parse incoming JSON request bodies (like the one we'll send to /api/mms/send).
  • Mount our mmsRoutes under the /api/mms prefix. So, the actual endpoint will be POST /api/mms/send.
  • Health Check: A simple /health endpoint is added as a best practice for monitoring.
  • Central Error Handling: This is a crucial piece. Any error passed via next(error) (like in our controller's catch block) will be caught here.
    • It logs the error (emphasizing that a real logger should be used in production).
    • It sets an appropriate HTTP status code (defaulting to 500 Internal Server Error).
    • It sends a standardized JSON error response to the client, avoiding leaking sensitive stack traces in production.
  • The server starts listening on the configured PORT.
  • Startup logs check for the presence of essential Plivo configuration from .env.
  • Note on Logging: This file also uses console.log and console.warn. As mentioned before, replace these with a dedicated logging library for production applications.

7. Security Considerations

While this guide covers basics, production systems require more robust security.

  • API Key Security: Your PLIVO_AUTH_ID and PLIVO_AUTH_TOKEN are highly sensitive.
    • NEVER commit them to version control. Use .env and .gitignore.
    • In production deployments, use secure secret management solutions provided by your cloud provider (e.g., AWS Secrets Manager, Google Secret Manager, Azure Key Vault) or tools like HashiCorp Vault instead of .env files.
  • Input Validation: We've implemented basic validation with express-validator. Ensure your validation rules are strict and cover all expected inputs to prevent injection attacks or unexpected behavior.
  • Rate Limiting: Protect your API endpoint (and your Plivo account balance) from abuse by implementing rate limiting. The express-rate-limit package is a popular choice. 
    npm install express-rate-limit
    Add it to app.js before your routes: 
    // src/app.js
const rateLimit = require('express-rate-limit');
// ... other imports

const limiter = rateLimit({
  windowMs: 15 * 60 * 1000, // 15 minutes
  max: 100, // Limit each IP to 100 requests per windowMs
  standardHeaders: true, // Return rate limit info in the `RateLimit-*` headers
  legacyHeaders: false, // Disable the `X-RateLimit-*` headers
  message: 'Too many requests from this IP, please try again after 15 minutes',
});

// Apply the rate limiting middleware to API calls
// Apply *before* the specific routes you want to limit
app.use('/api/mms', limiter); // Apply specifically to MMS routes

// --- Routes ---
app.use('/api/mms', mmsRoutes);
// ... rest of app.js
  • Authentication/Authorization: This guide doesn't include authentication. In a real application, you would protect the /api/mms/send endpoint so only authorized users or systems can trigger MMS sending (e.g., using API keys, JWT tokens, OAuth).
  • HTTPS: Always run your application behind a reverse proxy (like Nginx or Caddy) configured with TLS/SSL certificates (e.g., from Let's Encrypt) to ensure communication is encrypted. Do not run Node.js directly exposed to the internet on port 80/443.

8. Testing

Testing ensures your code works as expected and helps prevent regressions.

1. Unit Testing (Plivo Service): We can unit test the service layer by mocking the Plivo client.

Install Jest:

npm install --save-dev jest

Add a test script to package.json:

// package.json
{
  // ... other fields
  ""scripts"": {
    ""start"": ""node src/app.js"",
    ""test"": ""jest""
  },
  // ...
}

Create a test file src/services/plivoService.test.js:

// src/services/plivoService.test.js

// Mock the plivo module *before* importing the service
const mockCreate = jest.fn();
jest.mock('plivo', () =&gt; {
  // Mock the constructor and the messages.create method
  return {
    Client: jest.fn().mockImplementation(() =&gt; {
      // This is the instance returned by new plivo.Client()
      return {
        messages: {
          create: mockCreate,
        },
      };
    }),
  };
});

// Mock dotenv - prevent it from actually reading .env during tests
jest.mock('dotenv', () =&gt; ({
  config: jest.fn(),
}));

// Store original process.env
const OLD_ENV = process.env;

describe('Plivo Service', () =&gt; {
  beforeEach(() =&gt; {
    // Reset modules before each test to clear cache and re-require with fresh env vars
    jest.resetModules();
    // Clear mock function calls history
    mockCreate.mockClear();
    // Restore process.env and set default test values
    process.env = {
      ...OLD_ENV, // Preserve original env vars
      PLIVO_AUTH_ID: 'test-auth-id',
      PLIVO_AUTH_TOKEN: 'test-auth-token',
      PLIVO_SOURCE_NUMBER: '+15551112222',
    };
  });

  afterAll(() =&gt; {
    // Restore original environment variables after all tests
    process.env = OLD_ENV;
  });

  it('should call plivo.messages.create with correct parameters', async () =&gt; {
    // Re-require the service *inside the test* after setting env vars and resetting modules
    const plivoService = require('./plivoService');
    const dest = '+15553334444';
    const text = 'Test message';
    const mediaUrl = 'http://example.com/image.jpg';
    const expectedPlivoResponse = { messageUuid: 'some-uuid' };

    // Configure the mock to return a resolved promise
    mockCreate.mockResolvedValue(expectedPlivoResponse);

    const result = await plivoService.sendMms(dest, text, mediaUrl);

    // Assert that plivo.messages.create was called once
    expect(mockCreate).toHaveBeenCalledTimes(1);

    // Assert it was called with the correct arguments
    expect(mockCreate).toHaveBeenCalledWith(
      process.env.PLIVO_SOURCE_NUMBER, // src
      dest,                            // dst
      text,                            // text
      { type: 'mms', media_urls: [mediaUrl] } // options
    );

    // Assert the function returned the expected response
    expect(result).toEqual(expectedPlivoResponse);
  });

  it('should throw an error if Plivo API fails', async () =&gt; {
    // Re-require the service
    const plivoService = require('./plivoService');
    const dest = '+15553334444';
    const text = 'Test message';
    const mediaUrl = 'http://example.com/image.jpg';
    const expectedError = new Error('Plivo API Error');

    // Configure the mock to return a rejected promise
    mockCreate.mockRejectedValue(expectedError);

    // Assert that calling sendMms throws an error
    await expect(plivoService.sendMms(dest, text, mediaUrl))
      .rejects.toThrow('Plivo API Error');

    // Ensure plivo.messages.create was still called
    expect(mockCreate).toHaveBeenCalledTimes(1);
  });

  it('should throw an error if source number is not configured', async () =&gt; {
    // Modify environment for this specific test
    delete process.env.PLIVO_SOURCE_NUMBER;
    // Re-require the service *after* modifying env and resetting modules (via beforeEach)
    const plivoService = require('./plivoService');

    await expect(plivoService.sendMms('+111', 'txt', 'url'))
      .rejects.toThrow('Plivo source number is not configured in .env');
    // Ensure Plivo API was not called
    expect(mockCreate).not.toHaveBeenCalled();
  });

  it('should throw an error if auth credentials are not configured', async () =&gt; {
    // Modify environment for this specific test
    delete process.env.PLIVO_AUTH_ID;
     // Re-require the service *after* modifying env and resetting modules (via beforeEach)
    const plivoService = require('./plivoService');

    await expect(plivoService.sendMms('+111', 'txt', 'url'))
        .rejects.toThrow('Plivo Auth ID or Auth Token is missing in .env');
     // Ensure Plivo API was not called
    expect(mockCreate).not.toHaveBeenCalled();
  });
});

Run tests: npm test

Explanation of Test Changes:

  • jest.resetModules() is added to beforeEach to ensure that plivoService (and its dependency on process.env) is freshly loaded for each test, reflecting any changes made to process.env.
  • The service is now required inside each test case (or could be done once in beforeEach after setting process.env) to ensure the test uses the environment variables set for that specific test scope.
  • Added a test case for missing Auth ID/Token.

2. Integration Testing (API Endpoint): Test the full request-response cycle of your API endpoint.

Install Supertest:

npm install --save-dev supertest

Create a test file src/routes/mmsRoutes.test.js:

// src/routes/mmsRoutes.test.js

const request = require('supertest');
const app = require('../app'); // Import your configured Express app
const plivoService = require('../services/plivoService'); // Import to mock

// Mock the service layer to avoid actual Plivo calls during integration tests
// Jest automatically hoist jest.mock calls to the top of the module
jest.mock('../services/plivoService');

describe('MMS API Endpoint (/api/mms/send)', () =&gt; {
  beforeEach(() =&gt; {
    // Reset mocks before each test
    // Ensure the mock implementation is cleared or reset if needed
    // For jest.fn(), mockClear() is usually sufficient.
    plivoService.sendMms.mockClear();
  });

  it('should send MMS successfully with valid input', async () =&gt; {
    const requestBody = {
      destinationNumber: '+14155551234',
      text: 'Hello via API',
      mediaUrl: 'https://media.giphy.com/media/26gscSULUcfKU7dHq/source.gif',
    };
    const mockPlivoResponse = { message_uuid: ['mock-uuid-123'] };

    // Configure the mock service function to resolve successfully
    plivoService.sendMms.mockResolvedValue(mockPlivoResponse);

    const response = await request(app)
      .post('/api/mms/send')
      .send(requestBody)
      .expect('Content-Type', /json/)
      .expect(200);

    // Check if the service was called correctly
    expect(plivoService.sendMms).toHaveBeenCalledTimes(1);
    expect(plivoService.sendMms).toHaveBeenCalledWith(
      requestBody.destinationNumber,
      requestBody.text,
      requestBody.mediaUrl
    );

    // Check the response body
    expect(response.body.message).toEqual('MMS sending initiated successfully.');
    expect(response.body.plivoResponse).toEqual(mockPlivoResponse);
  });

  it('should return 400 Bad Request for invalid input (missing field)', async () =&gt; {
    const invalidRequestBody = {
      // destinationNumber is missing
      text: 'Missing number',
      mediaUrl: 'https://example.com/image.png',
    };

    const response = await request(app)
      .post('/api/mms/send')
      .send(invalidRequestBody)
      .expect('Content-Type', /json/)
      .expect(400);

    // Check the error response structure
    expect(response.body.errors).toBeDefined();
    expect(response.body.errors.length).toBeGreaterThan(0);
    expect(response.body.errors[0].path).toEqual('destinationNumber'); // Check which field failed
    expect(response.body.errors[0].msg).toContain('required'); // Check error message

    // Ensure the service was NOT called
    expect(plivoService.sendMms).not.toHaveBeenCalled();
  });

   it('should return 400 Bad Request for invalid URL format', async () =&gt; {
    const invalidRequestBody = {
      destinationNumber: '+14155551234',
      text: 'Bad URL',
      mediaUrl: 'not-a-valid-url', // Invalid URL
    };

    const response = await request(app)
      .post('/api/mms/send')
      .send(invalidRequestBody)
      .expect('Content-Type', /json/)
      .expect(400);

    expect(response.body.errors).toBeDefined();
    expect(response.body.errors[0].path).toEqual('mediaUrl');
    expect(response.body.errors[0].msg).toContain('valid URL');

    expect(plivoService.sendMms).not.toHaveBeenCalled();
  });


  it('should return 500 Internal Server Error if service throws an error', async () =&gt; {
    const requestBody = {
      destinationNumber: '+14155551234',
      text: 'This will fail',
      mediaUrl: 'https://example.com/fail.gif',
    };
    const errorMessage = 'Plivo service failed';

    // Configure the mock service to reject
    plivoService.sendMms.mockRejectedValue(new Error(errorMessage));

    const response = await request(app)
      .post('/api/mms/send')
      .send(requestBody)
      .expect('Content-Type', /json/)
      .expect(500);

    // Check the generic error response
    expect(response.body.message).toEqual('An unexpected error occurred.');
     // Optionally check error message in development
     // Note: Requires setting NODE_ENV=development for the test runner
     // if (process.env.NODE_ENV === 'development') {
     //    expect(response.body.error).toEqual(errorMessage);
     // }


    // Ensure the service was called
    expect(plivoService.sendMms).toHaveBeenCalledTimes(1);
  });
});

Run tests: npm test

9. Running the Application

  1. Ensure .env is correct: Double-check your PLIVO_AUTH_ID, PLIVO_AUTH_TOKEN, and PLIVO_SOURCE_NUMBER in the .env file.
  2. Start the server: 
    node src/app.js
    You should see output indicating the server is running and the configured source number.