HTTP Load Testing with Locust's HttpUser

Locust makes load testing web applications intuitive and efficient, thanks to its specialized HttpUser class. The HttpUser class provides built-in methods for HTTP interactions like GET, POST, PUT, and DELETE, making it an excellent choice for API and web application performance testing.

In this chapter, we’ll explore how to use the HttpUser class to perform HTTP GET requests with a simple example that tests a /todos endpoint.

What Is HttpUser?

The HttpUser class in Locust is a specialized user class designed for HTTP-based load testing. It includes the following features:

• A built-in HTTP client for making requests.

• Easy-to-use methods like get, post, and put for testing API endpoints.

• Support for handling headers, query parameters, and payloads.

By extending HttpUser, you can create users that simulate HTTP-based workflows for your application.

Example: HTTP GET Request with HttpUser

Here’s a simple example of an HttpUser that performs a GET request to retrieve a specific "todo" item from an API

from locust import HttpUser, constant, task

class MyReqRes(HttpUser):
    wait_time = constant(1)  # Wait 1 second between tasks
    host = "http://localhost:8001"  # Base URL for the API

    @task
    def get_todos(self):
        # Send a GET request to the "/todos/104" endpoint
        res = self.client.get("/todos/104")
        # Print the response text to the console
        print(res.text)

Explanation of the Code

1. MyReqRes Class

This class defines the behavior of a simulated user interacting with an API.

• HttpUser Base Class: Provides an HTTP client (self.client) for making requests.

• wait_time: The constant(1) function ensures the user waits 1 second between tasks.

• host: Sets the base URL for the API. All requests made by this user will use this host.

2. get_todos Task

This task sends a GET request to the /todos/104 endpoint. The response is printed to the console using print(res.text).

Enhancing the Example: Error Handling

To make the test more robust, you can include error handling to capture non-200 responses

from locust import HttpUser, constant, task

class MyReqRes(HttpUser):
    wait_time = constant(1)
    host = "http://localhost:8001"

    @task
    def get_todos(self):
        res = self.client.get("/todos/104")
        if res.status_code == 200:
            print(f"Success: {res.text}")
        else:
            print(f"Error {res.status_code}: {res.text}")

This ensures you’re informed about any issues during the test.

Adding Headers and Query Parameters

Locust’s HTTP client supports headers and query parameters, allowing you to test endpoints that require authentication or additional parameters. For example,

@task
def get_todos_with_params(self):
    headers = {"Authorization": "Bearer YOUR_TOKEN"}
    params = {"completed": "false"}
    res = self.client.get("/todos", headers=headers, params=params)
    print(res.text)

The HttpUser class in Locust is a powerful tool for load testing HTTP APIs. By using simple methods like get and post, you can simulate realistic user interactions with your application. Whether you’re testing a REST API or a web application backend, HttpUser provides the flexibility and ease of use to design and execute effective load tests.