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Postman API Testing Tips

How To Use Postman To Get Data From Api

API Testing Blog

Getting Started with Postman for API Testing

Postman is a powerful tool for working with APIs, especially for testing. It allows you to send requests, view responses, and even manage your API collections. This guide will walk you through how to use Postman to get data from APIs.

1. Setting Up Your Postman Environment

  1. Download and Install Postman: Head to the Postman website (https://www.postman.com/) and download the app for your operating system.
  2. Create an Account: Signing up for a free Postman account unlocks additional features like team collaboration and cloud storage for your work.
  3. Open Postman: Once installed, open the Postman application.

2. Choosing the Right API Endpoint

The endpoint is the specific URL you need to target within the API.

  • Example: Let’s say we want to get data from the popular “OpenWeatherMap” API to retrieve the current weather in London. The relevant endpoint is https://api.openweathermap.org/data/2.5/weather?q=London&appid=<YOUR_API_KEY>

    Note: You’ll need to replace <YOUR_API_KEY> with your actual OpenWeatherMap API key. You can get one by signing up for a free account on their website.

3. Making a GET Request in Postman

  1. Open a New Request: Click on the “New” button in the top-left corner of the Postman interface.
  2. Select “GET” Method: Choose the “GET” method from the dropdown menu.
  3. Enter the Endpoint: Paste your chosen API endpoint into the “Request URL” field.
  4. Add Headers (Optional): If the API requires headers (like an API key or authorization), click on the “Headers” tab and add them. For example, you could add an “X-API-Key” header with your API key, in the format {"X-API-Key": "<YOUR_API_KEY>"}.

4. Sending Your Request and Inspecting the Response

  1. Send the Request: Click the “Send” button at the top right of the Postman window.
  2. View the Response: The response from the API will be displayed in the bottom panel.
    • Status Code: Look for the HTTP status code (e.g., 200 - OK). This indicates if the request was successful.
    • Headers: Examine the response headers, which provide additional information about the response.
    • Body: The most important part for retrieving data is the response body. This is where the API data will be returned.

5. Understanding Response Formats & Data Parsing

APIs typically return data in structured formats like JSON or XML:

  • JSON: A common format designed for human-readable data exchange and easy parsing. You can easily view JSON data within Postman and navigate the structure.
  • XML: Another standardized format that uses tags to structure data.

Example with JSON: In the OpenWeatherMap API, the response data for London weather is likely to be in JSON format. Postman will automatically display it in a user-friendly format. You can then easily access specific data points like “temperature”, “humidity”, or “description” of the weather using the keys in the JSON structure.

Code Example (JSON):

{
  "coord": {
    "lon": -0.1257,
    "lat": 51.5074
  },
  "weather": [
    {
      "id": 800,
      "main": "Clear",
      "description": "clear sky",
      "icon": "01d"
    }
  ],
  "main": {
    "temp": 282.55,
    "feels_like": 278.92,
    "temp_min": 280.15,
    "temp_max": 285.15,
    "pressure": 1018,
    "humidity": 77
  },
  // ... other data fields ...
}

6. Using Postman’s Features for Efficient API Testing

Postman Collection: Organize your API requests into collections for easy management. This allows you to group related API calls, including tests and documentation.

Environment Variables: Store API keys, base URLs, and other sensitive information in environment variables instead of hardcoding them directly in your requests. This makes it easier to change configurations and collaborate with your team.

Pre-request Scripts: Perform actions before sending a request, such as setting variables or modifying headers. This is useful for dynamic testing scenarios.

Tests: Write test scripts in the “Tests” tab to verify the API response against your expectations. This ensures the API is behaving as intended.

Example of a Test in Postman:

pm.test("Status code is 200", function () {
  pm.response.to.have.status(200); // Verify that the response status is 200 (OK)
});


pm.test("Response contains 'London'", function () {
  pm.expect(pm.response.text()).to.include('London');  // Check if 'London' is present in the response body
});

Postman Runner: Run your collected tests automatically and track their execution results. This helps you monitor the health and reliability of your APIs.

By leveraging these features, Postman transforms from a simple tool for making requests into a robust platform for comprehensive API testing and management.

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