[Python] Getting "SessionNotCreatedException" error while running selenium tests in docker...

I have my test automation framework built using Selenium with Python, and I'm trying to execute my tests in a container using docker. While doing so I'm getting "SessionNotCreatedException"

When I run my code on my laptop it runs fine, however fails when executing them in a container

Things that I have tried (after asking chatgpt/gemini/claude:

• Setting some fresh new temporary directory options.add_argument(f'--user-data-dir={user_data_dir}'), where variable user_data_dir is some randomly generated temporary directory

Please find below the contents from different files (code snippets), and the entire error stacktrace

test_dockerized_tests.py

from selenium.webdriver import Chrome
from selenium.webdriver.chrome.options import Options as chrome_options

class TestDockerized:

def test_selenium_visit_a_site_and_validate(self):
options = chrome_options()
options.add_argument("--headless")
# options.add_argument('--incognito')
# options.add_argument('--disable-dev-shm-usage')
driver = Chrome(options=options)
driver.get('https://example.com')
expected_title = 'Example Domain'
actual_title = driver.title
assert actual_title == expected_title


Dockerfile

FROM python:3.12

WORKDIR /practice-python

RUN apt-get update && apt-get install -y \
wget \
unzip \
curl \
gnupg \
ca-certificates \
fonts-liberation \
libasound2 \
libatk-bridge2.0-0 \
libatk1.0-0 \
libcups2 \
libdbus-1-3 \
libgdk-pixbuf2.0-0 \
libnspr4 \
libnss3 \
libx11-xcb1 \
libxcomposite1 \
libxdamage1 \
libxrandr2 \
xdg-utils \
git \
chromium \
--no-install-recommends && rm -rf /var/lib/apt/lists/*

COPY requirements.txt .

RUN pip install --upgrade pip && \
pip install --no-cache-dir -r requirements.txt

COPY . .

ENV CHROME_BIN=/usr/bin/chromium
ENV CHROMEDRIVER_PATH=/usr/bin/chromedriver

CMD ["pytest", "-rA", "-v", "tests/test_dockerized_tests.py"]


requirements.txt

selenium==4.27.1
playwright==1.49.0

pytest==8.3.3
pytest-xdist==3.6.1
pytest-html==4.1.1
pytest-playwright==0.6.2
pytest-base-url==2.1.0
pytest-asyncio==0.25.0
python-dotenv==1.0.1
pytest-rerunfailures
allure-pytest==2.13.5

requests==2.32.3
urllib3==2.2.3
# psycopg2==2.9.10
psycopg2-binary==2.9.10
typing_extensions==4.12.2


Error stacktrace

============================= test session starts ==============================
platform linux -- Python 3.13.3, pytest-8.3.3, pluggy-1.5.0 -- /usr/local/bin/python3.13
cachedir: .pytest_cache
metadata: {'Python': '3.13.3', 'Platform': 'Linux-6.11.0-1012-azure-x86_64-with-glibc2.36', 'Packages': {'pytest': '8.3.3', 'pluggy': '1.5.0'}, 'Plugins': {'rerunfailures': '15.0', 'xdist': '3.6.1', 'html': '4.1.1', 'allure-pytest': '2.13.5', 'base-url': '2.1.0', 'metadata': '3.1.1', 'playwright': '0.6.2', 'asyncio': '0.25.0'}, 'Base URL': ''}
rootdir: /practice-python
plugins: rerunfailures-15.0, xdist-3.6.1, html-4.1.1, allure-pytest-2.13.5, base-url-2.1.0, metadata-3.1.1, playwright-0.6.2, asyncio-0.25.0
asyncio: mode=Mode.STRICT, asyncio_default_fixture_loop_scope=None
collecting ... collected 1 items

tests/test_dockerized_tests.py::TestDockerized::test_selenium_visit_a_site_and_validate FAILED [100%]

=================================== FAILURES ===================================
____________ TestDockerized.test_selenium_visit_a_site_and_validate ____________

self = <tests.test_dockerized_tests.TestDockerized object at 0x7fb24ee7ead0>

def test_selenium_visit_a_site_and_validate(self):
# driver = get_selenium_driver
# driver.get('https://example.com')
# expected_title = 'Example Domain'
# actual_title = driver.title
# print(f'Actual title = {actual_title}')
# assert actual_title == expected_title

options = chrome_options()
options.add_argument("--headless")
# options.add_argument('--incognito')
# options.add_argument('--disable-dev-shm-usage')
> driver = Chrome(options=options)

tests/test_dockerized_tests.py:20:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
/usr/local/lib/python3.13/site-packages/selenium/webdriver/chrome/webdriver.py:45: in __init__
super().__init__(
/usr/local/lib/python3.13/site-packages/selenium/webdriver/chromium/webdriver.py:66: in __init__
super().__init__(command_executor=executor, options=options)
/usr/local/lib/python3.13/site-packages/selenium/webdriver/remote/webdriver.py:241: in __init__
self.start_session(capabilities)
/usr/local/lib/python3.13/site-packages/selenium/webdriver/remote/webdriver.py:329: in start_session
response = self.execute(Command.NEW_SESSION, caps)["value"]
/usr/local/lib/python3.13/site-packages/selenium/webdriver/remote/webdriver.py:384: in execute
self.error_handler.check_response(response)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <selenium.webdriver.remote.errorhandler.ErrorHandler object at 0x7fb24ed09940>
response = {'status': 500, 'value': '{"value":{"error":"session not created","message":"session not created: probably user data d...\\n#15 0x55fe3c8d9856 \\u003Cunknown>\\n#16 0x55fe3c8ea666 \\u003Cunknown>\\n#17 0x7fdda00c11f5 \\u003Cunknown>\\n"}}'}

def check_response(self, response: Dict[str, Any]) -> None:
"""Checks that a JSON response from the WebDriver does not have an
error.

:Args:
- response - The JSON response from the WebDriver server as a dictionary
object.

:Raises: If the response contains an error message.
"""
status = response.get("status", None)
if not status or status == ErrorCode.SUCCESS:
return
value = None
message = response.get("message", "")
screen: str = response.get("screen", "")
stacktrace = None
if isinstance(status, int):
value_json = response.get("value", None)
if value_json and isinstance(value_json, str):
import json

try:
value = json.loads(value_json)
if len(value) == 1:
value = value["value"]
status = value.get("error", None)
if not status:
status = value.get("status", ErrorCode.UNKNOWN_ERROR)
message = value.get("value") or value.get("message")
if not isinstance(message, str):
value = message
message = message.get("message")
else:
message = value.get("message", None)
except ValueError:
pass

exception_class: Type[WebDriverException]
e = ErrorCode()
error_codes = [item for item in dir(e) if not item.startswith("__")]
for error_code in error_codes:
error_info = getattr(ErrorCode, error_code)
if isinstance(error_info, list) and status in error_info:
exception_class = getattr(ExceptionMapping, error_code, WebDriverException)
break
else:
exception_class = WebDriverException

if not value:
value = response["value"]
if isinstance(value, str):
raise exception_class(value)
if message == "" and "message" in value:
message = value["message"]

screen = None # type: ignore[assignment]
if "screen" in value:
screen = value["screen"]

stacktrace = None
st_value = value.get("stackTrace") or value.get("stacktrace")
if st_value:
if isinstance(st_value, str):
stacktrace = st_value.split("\n")
else:
stacktrace = []
try:
for frame in st_value:
line = frame.get("lineNumber", "")
file = frame.get("fileName", "<anonymous>")
if line:
file = f"{file}:{line}"
meth = frame.get("methodName", "<anonymous>")
if "className" in frame:
meth = f"{frame['className']}.{meth}"
msg = " at %s (%s)"
msg = msg % (meth, file)
stacktrace.append(msg)
except TypeError:
pass
if exception_class == UnexpectedAlertPresentException:
alert_text = None
if "data" in value:
alert_text = value["data"].get("text")
elif "alert" in value:
alert_text = value["alert"].get("text")
raise exception_class(message, screen, stacktrace, alert_text) # type: ignore[call-arg] # mypy is not smart enough here
> raise exception_class(message, screen, stacktrace)
E selenium.common.exceptions.SessionNotCreatedException: Message: session not created: probably user data directory is already in use, please specify a unique value for --user-data-dir argument, or don't use --user-data-dir
E Stacktrace:
E #0 0x55fe3c8eb7fa <unknown>
E #1 0x55fe3c38fe90 <unknown>
E #2 0x55fe3c3c9cfb <unknown>
E #3 0x55fe3c3c5a3f <unknown>
E #4 0x55fe3c415c15 <unknown>
E #5 0x55fe3c415136 <unknown>
E #6 0x55fe3c407013 <unknown>
E #7 0x55fe3c3d3b3b <unknown>
E #8 0x55fe3c3d47a1 <unknown>
E #9 0x55fe3c8b0b9b <unknown>
E #10 0x55fe3c8b4a8a <unknown>
E #11 0x55fe3c898912 <unknown>
E #12 0x55fe3c8b5604 <unknown>
E #13 0x55fe3c87d74f <unknown>
E #14 0x55fe3c8d9678 <unknown>
E #15 0x55fe3c8d9856 <unknown>
E #16 0x55fe3c8ea666 <unknown>
E #17 0x7fdda00c11f5 <unknown>

/usr/local/lib/python3.13/site-packages/selenium/webdriver/remote/errorhandler.py:232: SessionNotCreatedException
==================================== PASSES ====================================
___________ TestDockerized.test_playwright_visit_a_site_and_validate ___________
----------------------------- Captured stdout call -----------------------------
Actual title = Example Domain
---------------- Generated html report: file:///practice-python/report.html ----------------
=========================== short test summary info ============================
FAILED tests/test_dockerized_tests.py::TestDockerized::test_selenium_visit_a_site_and_validate
========================= 1 failed in 1.28s ==========================
Error: Process completed with exit code 1

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