[pypi test drive] Locust (performance testing tool) - updated at 2021-12-23

Locust

Locust claims to be:

an easy to use, scriptable and scalable performance testing tool.

and to be more specific:

You define the behaviour of your users in regular Python code, instead of using a clunky UI or domain specific language

and the features include:

• Write user test scenarios in plain old Python
• Distributed & Scalable - supports hundreds of thousands of users
• Web-based UI
• Can test any system
• Hackable

Fact check

pypi	locust
version	2.5.1 (as of 2021-12-23)
source	github
documentation	https://docs.locust.io/
minimum python ver	3.6

Test drive environment

OS	Windows 10 Home 21H1 19043.1081
python	3.9.6; MSC v.1929 64 bit (AMD64)
pip	21.3.1

Package dependencies (after pip install)

python -m pip install locust==2.5.1
python -m pip list

gives:

Package            Version
------------------ ---------
Brotli             1.0.9
certifi            2021.10.8
cffi               1.15.0
charset-normalizer 2.0.9
click              8.0.3
colorama           0.4.4
ConfigArgParse     1.5.3
Flask              2.0.2
Flask-BasicAuth    0.2.0
Flask-Cors         3.0.10
gevent             21.12.0
geventhttpclient   1.5.3
greenlet           1.1.2
idna               3.3
itsdangerous       2.0.1
Jinja2             3.0.3
locust             2.5.1
MarkupSafe         2.0.1
msgpack            1.0.3
pip                21.3.1
psutil             5.8.0
pycparser          2.21
pywin32            303
pyzmq              22.3.0
requests           2.26.0
roundrobin         0.0.2
setuptools         60.0.4
six                1.16.0
typing_extensions  4.0.1
urllib3            1.26.7
Werkzeug           2.0.2
zope.event         4.5.0
zope.interface     5.4.0

Test drive

Setup target web application (flask):

# app.py

from flask import Flask


app = Flask(__name__)


@app.route("/")
def home() -> str:
    return "<p>Hellow world!</p>"


@app.route("/<int:number>")
def lucky_number(number: int) -> str:
    return f"<p>Your lucky number is {number}!</p>"

and:

python -m flask run

Then the terminal shows:

 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: off
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)

Setup test runner:

# runner.py

import random
from typing import Callable

from locust import HttpUser, between, task


class FlaskAppUser(HttpUser):
    wait_time: Callable = between(min_wait=1, max_wait=3)

    # Overwrite this to customize initial behavior
    def on_start(self) -> None:
        return super().on_start()

    @task(weight=3)
    def go_home(self) -> None:
        self.client.get("/")

    @task(weight=1)
    def go_lucky_number(self) -> None:
        for _ in range(10):
            self.client.get(f"/{random.randint(100, 999)}")

and:

python -m locust -f runner.py

Then the terminal shows:

[2021-08-16 ******] DESKTOP-******/INFO/locust.main: Starting web interface at http://0.0.0.0:8089 (accepting connections from all network interfaces)
[2021-08-16 ******] DESKTOP-******/INFO/locust.main: Starting Locust 2.1.0

Run the test:

Go to http://localhost:8089/ in the browser and the locust page is shown, fill in the desired parameter as well as the host of the target flask app:

Click Start swarming button in the page and the test starts to run, and the statistics are populated in real time:

The Charts tab shows graphs:

At any time, click the STOP botton on top-right corner to stop the current run.
The terminal in which the runner runs shows like:

[2021-08-16 ******] DESKTOP-******/INFO/locust.runners: Ramping to 10 users at a rate of 10.00 users per second
[2021-08-16 ******] DESKTOP-******/INFO/locust.runners: All users spawned: {"FlaskAppUser": 10} (10 total users)