Bonus Tutorial: API Testing with Postman

Bonus Tutorial: API Testing with Postman – Why & How? 🚀

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📌 Why Should You Test APIs Before Frontend Integration?

Before integrating APIs into the frontend, it’s critical to test them independently. Here’s why:

✅ Early Bug Detection – Find API issues before they affect the UI.
✅ Faster Debugging – Identify if an issue is in the backend or frontend.
✅ Smoother Integration – Ensure API responses match frontend expectations.
✅ Security Testing – Test authentication, roles, and protected routes.
✅ Automation Ready – Save test cases for future automated testing.

Instead of constantly switching between frontend & backend, Postman lets you test APIs efficiently before connecting them.

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🔧 Getting Started with Postman

1️⃣ Install Postman

1. Download & install Postman.
2. Open the Postman app and create a free account (optional but useful for saving requests).

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🚀 Testing Flask API with Postman

We will test the following API endpoints:

• User Signup
• User Login
• Protected API (JWT Authentication)
• CRUD Operations: Tasks Management
• Role-Based Access Control (Admin & Manager Actions)

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1️⃣ Testing User Signup API

📌 Endpoint: POST http://127.0.0.1:5000/signup

🔹 Steps in Postman:

1. Open Postman and select POST request.
2. Enter the API URL:

   http://127.0.0.1:5000/signup
   

3. Go to the Body tab → Select raw → Choose JSON.
4. Enter this JSON data:

   {
     "username": "testuser",
     "email": "testuser@example.com",
     "password": "testpassword"
   }
   

5. Click Send and check the response.

✅ Expected Response:

{
  "username": "testuser",
  "email": "testuser@example.com"
}

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2️⃣ Testing User Login & Generating JWT Token

📌 Endpoint: POST http://127.0.0.1:5000/login

🔹 Steps in Postman:

1. Select POST request.
2. URL:

   http://127.0.0.1:5000/login
   

3. Body → raw → Select JSON and enter:

   {
     "email": "testuser@example.com",
     "password": "testpassword"
   }
   

4. Click Send.

✅ Expected Response (with JWT Token):

{
  "msg": "successfully logged in",
  "token": "eyJhbGciOiJIUzI1..."
}

⚡ Copy the JWT token – You’ll need it for testing protected APIs.

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3️⃣ Testing Protected API with JWT Authentication

📌 Endpoint: GET http://127.0.0.1:5000/hello

🔹 Steps in Postman:

1. Select GET request.
2. Enter URL:

   http://127.0.0.1:5000/hello
   

3. Go to Headers tab.
4. Add a new header:
   • Key: Authorization
   • Value: Bearer <JWT-TOKEN>
     (Replace <JWT-TOKEN> with the token copied earlier.)
5. Click Send.

✅ Expected Response:

{
  "msg": "hello world! from flask restful",
  "user_name": "testuser"
}

🚀 If you don’t send a valid JWT, it returns 401 Unauthorized.

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4️⃣ Creating a Task (Admin/Manager Only)

📌 Endpoint: POST http://127.0.0.1:5000/tasks

🔹 Steps in Postman:

1. Select POST request.
2. URL:

   http://127.0.0.1:5000/tasks
   

3. Headers → Add Authorization Header:

   Authorization: Bearer <JWT-TOKEN>
   

4. Body → raw → JSON:

   {
     "title": "Fix Backend Bug",
     "description": "Resolve API timeout issue",
     "deadline": "2025-02-20"
   }
   

5. Click Send.

✅ Expected Response:

{
  "message": "Task created successfully"
}

📌 If the user isn’t an admin/manager, it returns:

{
  "message": "Unauthorized access"
}

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5️⃣ Fetching All Tasks (Admin/Manager Only)

📌 Endpoint: GET http://127.0.0.1:5000/tasks

🔹 Steps in Postman:

1. Select GET request.
2. URL:

   http://127.0.0.1:5000/tasks
   

3. Headers → Add Authorization Header:

   Authorization: Bearer <JWT-TOKEN>
   

4. Click Send.

✅ Expected Response:

[
  {
    "id": 1,
    "title": "Fix Backend Bug",
    "description": "Resolve API timeout issue",
    "status": "pending",
    "deadline": "2025-02-20"
  }
]

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6️⃣ Assigning a Task to a User (Manager Only)

📌 Endpoint: PUT http://127.0.0.1:5000/task/1/assign

🔹 Steps in Postman:

1. Select PUT request.
2. URL:

   http://127.0.0.1:5000/task/1/assign
   

3. Headers → Add Authorization Header:

   Authorization: Bearer <JWT-TOKEN>
   

4. Body → raw → JSON:

   {
     "user_id": 2
   }
   

5. Click Send.

✅ Expected Response:

{
  "message": "Task assigned successfully"
}

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7️⃣ Viewing API Stats (Admin/Manager Only)

📌 Endpoint: GET http://127.0.0.1:5000/stats

🔹 Steps in Postman:

1. Select GET request.
2. URL:

   http://127.0.0.1:5000/stats
   

3. Headers → Add Authorization Header:

   Authorization: Bearer <JWT-TOKEN>
   

4. Click Send.

✅ Expected Response:

{
  "total_users": 5,
  "total_tasks": 10,
  "completed_tasks": 3
}

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Feature	Postman API Testing	Frontend Integration
Faster Debugging	✅ Directly test backend	❌ Requires UI interactions
Error Identification	✅ Isolates API errors	❌ Hard to debug API issues
Role-Based Testing	✅ Easily switch tokens	❌ Requires logging in/out
Security Testing	✅ Test unauthorized access	❌ Harder to simulate
Automated Testing	✅ Save requests & automate	❌ Requires frontend setup
No UI Dependency	✅ Works standalone	❌ Needs UI components

🔹 Conclusion: Testing APIs with Postman before frontend integration makes development smoother, debugging faster, and reduces errors before they impact users! 🚀🔥

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📌 Next Steps

• 🔥 Automate Postman tests using Pre-Request Scripts
• 📊 Learn API monitoring with Postman Collections
• 🛠️ Integrate APIs with React/Angular Frontend

Happy Testing! 🚀🎯