Coderead: Locust

• Github

• Load testing tool written in Python

• Simple makefile
• Uses vagrant to create a local vm for testing
• Uses flask for a web admin ui
  • TIL flask has extensions for cors, basicauth!
  • eg Extension naming convention flask-basicauth
• locust/web.py has the flask webapp
  • Very nicely factored
  • Not an SPA. Templating language used (jinja2?) with server side rendering (SSR). I guess you can still build apps this way! It saves a bunch of complexity setting up build tools for an asset pipeline if the framework you’re using doesn’t give you that for free which flask does not I guess
• Bumped into type hinting today again. It’s been awhile since I’ve read python code so it took a few minutes to get myself oriented :)
  • Interesting that code docs appear after symbols … :/

class WebUI:
    """
    Sets up and runs a Flask web app that can start and stop load tests using the
    :attr:`environment.runner <locust.env.Environment.runner>` as well as show the load test statistics
    in :attr:`environment.stats <locust.env.Environment.stats>`
    """

    app: Optional[Flask] = None
    """
    Reference to the :class:`flask.Flask` app. Can be used to add additional web routes and customize
    the Flask app in other various ways. Example::
        from flask import request
        @web_ui.app.route("/my_custom_route")
        def my_custom_route():
            return "your IP is: %s" % request.remote_addr
    """

    greenlet: Optional[gevent.Greenlet] = None
    """
    Greenlet of the running web server
    """
    
    ...

• Here’s the task decorator where we describe load test user scripts

def task(weight: TaskT | int = 1) -> TaskT | Callable[[TaskT], TaskT]:
    """
    Used as a convenience decorator to be able to declare tasks for a User or a TaskSet
    inline in the class. Example::
        class ForumPage(TaskSet):
            @task(100)
            def read_thread(self):
                pass
            @task(7)
            def create_thread(self):
                pass
            @task(25)
            class ForumThread(TaskSet):
                @task
                def get_author(self):
                    pass
                @task
                def get_created(self):
                    pass
    """

    def decorator_func(func):
        if func.__name__ in ["on_stop", "on_start"]:
            logging.warning(
                "You have tagged your on_stop/start function with @task. This will make the method get called both as a task AND on stop/start."
            )  # this is usually not what the user intended
        if func.__name__ == "run":
            raise Exception(
                "User.run() is a method used internally by Locust, and you must not override it or register it as a task"
            )
        func.locust_task_weight = weight
        return func

    """
    Check if task was used without parentheses (not called), like this::
        @task
        def my_task()
            pass
    """
    if callable(weight):
        func = weight
        weight = 1
        return decorator_func(func)
    else:
        return decorator_func