In this tutorial, we’ll create a basic API testing framework using Postman. We’ll cover setting up environment variables, organizing tests into collections, creating reusable scripts, and running tests in an automated manner.
1. Collections and Environments
- Collections: Organize your API requests into logical groups based on functionality. You can create a collection for user management, another for product management, and so on.
- Environments: Store reusable variables like base URLs, API keys, or database connections. This allows you to easily switch between different testing environments (development, staging, production) without modifying requests.
Set Up Environments Variables
- Click on the gear icon in the top right corner of Postman and select “Manage Environments.”
- Click on “Add” to create a new environment.
- Enter a name for your environment and add key-value pairs for your variables (e.g., base URL, authentication tokens).
- Click “Add” to save your environment.
Organizing requests in Collections
- Click on the “Collections” tab in Postman.
- Click on “New Collection” to create a new collection.
- Enter a name for your collection and click “Create.”
- Click on your collection to open it.
- Click on “Add Request” to add a new request to your collection.
- Enter a name for your request and select the HTTP method (e.g., GET, POST, PUT, DELETE).
- Enter the URL for your API endpoint and click “Save to [your collection name].”
- Repeat steps 5-7 to add more requests to your collection.
2. Building Test Cases:
- Define Requests: Create individual requests within your collections using various HTTP methods (GET, POST, PUT, DELETE) and specify the URL, headers, body (if applicable), and authentication details.
- Write Tests: Postman’s Test Scripting allows you to write assertions to verify the API response. You can check for expected status codes, validate response body content using JSONPath or similar expressions, and ensure data integrity. Popular options for writing tests include:
- Built-in snippets: Postman offers pre-written code snippets for common assertions like checking status codes or response body content.
- JavaScript (with Chai library): For more complex assertions and manipulations, you can leverage JavaScript and the Chai assertion library.
Create Reusable Scripts
- Click on a request in your collection to open it.
- Click on the “Tests” tab below the request URL.
- Write JavaScript code to perform tests on the response (e.g., check status code, response body).
- Use environment variables in your scripts by referencing them with
pm.environment.get('variable_name'). - Click “Save” to save your script.
In Postman, you can write JavaScript code to perform tests on the response using the built-in testing framework. Here’s an example of how you can write tests to check the status code and response body of a request:
// Test for a successful response (status code 200)
pm.test("Status code is 200", function () {
pm.response.to.have.status(200);
});
// Test for a specific header in the response
pm.test("Content-Type is present", function () {
pm.response.to.have.header("Content-Type");
});
// Test for a specific value in the response body
pm.test("Response body contains 'success'", function () {
pm.expect(pm.response.text()).to.include("success");
});
// Test for a specific JSON value in the response body
pm.test("JSON response body contains 'value'", function () {
var jsonData = pm.response.json();
pm.expect(jsonData.value).to.eql("expected_value");
});
In this example, pm.test is used to define a test, and pm.response.to.have and pm.expect are used to make assertions on the response. You can add these tests to the “Tests” tab of your request in Postman to run them when the request is executed.
3. Running and Automating Tests
- Collection Runner: Execute your entire collection of tests at once. You can set delays between requests to simulate real-world usage and configure iterations for load testing.
- Newman: For command-line automation, Newman allows you to run your Postman collections from the terminal. This enables integration with continuous integration (CI) pipelines for automated API testing during the development lifecycle.
Run Tests Manually
- Click on the collection you want to test.
- Click on the “Run” button.
- Select the environment you want to use (if you set up environment variables).
- Click “Run [your collection name]” to run your tests manually.
Automate Tests with Newman
Install Newman using npm (Node Package Manager) if you haven’t already:
npm install -g newman
- Export your collection and environment variables as JSON files:
- Click on the ellipsis (…) next to your collection name.
- Select “Export” and choose “Collection v2” to export your collection.
- Repeat the process for your environment variables.
- Run your collection using Newman:
newman run your-collection.json -e your-environment.json
Replace your-collection.json with the path to your exported collection JSON file and your-environment.json with the path to your exported environment JSON file.
Additional Tips:
- Pre-request Scripts: Utilize pre-request scripts to dynamically modify requests based on variables or environment data. This helps create reusable and maintainable tests.
- Environments and Global Variables: Separate environment-specific variables from globally used ones to keep your tests organized and adaptable.
- Documentation: Postman allows you to document your API requests and tests. This improves collaboration and understanding for developers and testers.
By following these steps and leveraging Postman’s features, you can build a robust and efficient API testing framework to ensure the quality and functionality of your APIs.