How To Create An Api Using Postman

Harnessing Postman: A Comprehensive Guide to Creating APIs for Testers

Postman, a versatile tool for API development and testing, offers a powerful yet intuitive way to create your own APIs. Whether you’re crafting a mock API for testing or building a robust API for use in a project, Postman provides all the tools you need.

Let’s dive into the practical details of how to create APIs using Postman, armed with step-by-step instructions and illustrative code examples.

Crafting Your First API: A Simple Example

This section guides you through building a basic “Hello World” API using Postman.

Start with Collections: In Postman, collections organize your API requests, making it easier to manage and share. Create a new collection named “Hello World API.”
Create a Request: Within your collection, add a new request called “Get Hello Message.” Select the “GET” method for your request, as a GET request retrieves data.
Specify the Endpoint: In the “Enter request URL” field, type {{url}}/hello. This placeholder {{url}} will be replaced later with a specific URL when you actually run your API.
Define Test Scripts: Postman’s test scripts are JavaScript snippets that automatically verify your API responses. Click “Tests” and add the following code:
```
pm.test("Status code is 200", function () {
    pm.response.to.have.status(200);
});

pm.test("Response contains Hello World", function () {
    pm.expect(pm.response.text()).to.include("Hello World");
});
```
This script checks if the response code is 200 (successful) and if the response text includes “Hello World”.
Set Up Environment Variables: To make your API flexible, we’ll use an environment variable for the base URL. Click the “Environment” button and create a new environment named “My API.” Add a variable called url and set its value to https://your-api-host.com. This placeholder URL will be used in the “Get Hello Message” request.
Run Your API: Switch to the “My API” environment and click “Send” on your “Get Hello Message” request. Postman sends the GET request to your API and executes the test scripts. If everything is successful, you’ll see the green test icons with “Passed” labels.
Add More Functionality: Let’s create another request to handle different greetings. Add a new “POST” request to the collection called “Post Greeting”. Modify the endpoint to {{url}}/greeting, and in the “Body” section, set the “Body Type” to “raw” and the “raw” format to “JSON.” Provide a sample JSON body with a “message” field:
```
{
    "message": "Good Day!"
}
```
Add the following test scripts:
```
pm.test("Status code is 200", function () {
    pm.response.to.have.status(200);
});

pm.test("Response body contains message", function () {
    pm.expect(pm.response.json()).to.have.property('message');
});
```

Handling Request Parameters: Enhancing API Flexibility

Now that you have basic requests, it’s time to add parameters to make your API more dynamic.

Adding Query Parameters: Let’s modify the “Get Hello Message” request to handle a name parameter. In the “Params” tab, add a new parameter named “name” and set its value to {{name}}.

Dynamic Test Script: Update your test script to verify the presence of the name in the response:

pm.test("Status code is 200", function () {
    pm.response.to.have.status(200);
});

pm.test("Response contains Hello World", function () {
    pm.expect(pm.response.text()).to.include("Hello World");
});

pm.test("Response includes name", function () {
    pm.expect(pm.response.text()).to.include(pm.variables.get("name"));
});

Setting Up the Environment: In your “My API” environment, add a new variable named “name” and set its value to the desired name.
Running with Parameters: When you run the “Get Hello Message” request, Postman will automatically replace {{name}} in the URL with the value you set in your environment. The test script will then verify that the response includes this dynamic name.

Crafting Mock APIs for Testing

Postman empowers you to create mock APIs that mimic the behavior of real APIs, crucial for testing applications before the real APIs are ready.

Mock Responses: In your request, switch to the “Mock” tab and choose “Mock responses.” Click “Add a mock response” and provide a sample JSON response:
```
{
  "message": "This is a mock response!"
}
```
Mock Servers: Postman also lets you create mock servers. In the “Mock” tab, choose “Mock server options.” Generate a mock server for your API. This server will accept requests and respond with your mock responses.
Test Against the Mock API: Now, in your test scripts, instead of referencing pm.response, you can access the mock responses using pm.mockResponse to test your application against the mock API.

Postman facilitates easy sharing and versioning to collaborate with your team.

Exporting Your Work: You can export your collection and environment as a JSON file for sharing.
Importing Collections: With the imported JSON, others can access your API endpoints and use your test scripts.
Version Control: Postman integrates with version control systems like GitHub. This allows you to track changes, collaborate, and ensure everyone has access to the latest iteration of the API.

Building a Secure API: Adding Authentication

Security is paramount for any API.

Authentication Basics: Postman supports various authentication mechanisms, including API keys, OAuth, and Basic Authentication.
Setting Up Authentication: In the “Authorization” tab, select your preferred authentication method and provide the required credentials. Postman will automatically include these credentials in your requests, ensuring secure communication.

These are just the foundational elements of creating APIs in Postman. As your requirements grow, you can explore advanced features like writing custom code, using pre-request and test scripts for complex logic, and collaborating on API development in teams.

With Postman’s rich toolbox, you’re well-equipped to build robust, secure, and well-tested APIs, contributing to the seamless integration of software components in your projects. Remember to practice and experiment with these features to unlock the full potential of Postman in your API development journey.