Match ChromeDriver to Chrome to avoid SessionNotCreatedException

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Summary

A Selenium test failed because ChromeDriver 146 was used against Chrome 145. The mismatch prevented the driver from establishing a session, resulting in a SessionNotCreatedException.

Root Cause

  • Version incompatibility between Chrome browser and ChromeDriver.
  • ChromeDriver is tightly coupled to a specific major Chrome version; it rejects connections to older browsers.
  • The developer was manually downloading the latest driver without checking the installed browser version.

Why This Happens in Real Systems

  • Chrome auto‑updates on some machines but not on others (policy, corporate firewalls, or user settings).
  • Teams often pin a driver version in CI pipelines; when a browser is upgraded independently, the pin becomes stale.
  • Selenium’s error message is precise but can be overlooked by newcomers who focus on the stack trace instead of the version numbers.

Real-World Impact

  • Test suites stop running in CI/CD pipelines, causing blocked releases.
  • Debug time increases as engineers chase log lines that appear unrelated to version numbers.
  • Customer‑facing automation (e.g., UI health checks) fails, potentially triggering false alarms.

Example or Code (if necessary and relevant)

from selenium import webdriver
from selenium.webdriver.chrome.service import Service

service = Service(executable_path="/path/to/chromedriver")
options = webdriver.ChromeOptions()
driver = webdriver.Chrome(service=service, options=options)

driver.get("https://example.com")
print(driver.title)
driver.quit()

The code itself is correct; the failure stems solely from the driver‑browser version mismatch.

How Senior Engineers Fix It

  • Pin matching versions in a configuration file or environment variable.
  • Automate driver download using tools like webdriver-manager or playwright that sync versions.
  • Add a pre‑run sanity check:
    • Query Chrome version (chrome://version/ or google-chrome --version).
    • Compare with ChromeDriver’s --version output.
    • Abort with a clear error if they differ.
  • Keep browser updates under control in production/staging environments (e.g., use a locked Chrome version Docker image).

Why Juniors Miss It

  • Tend to read the stack trace and assume a code bug, ignoring the version numbers highlighted in the exception.
  • May not be familiar with the tight coupling between ChromeDriver and Chrome versions.
  • Often lack experience with environment consistency practices (pinning, CI checks, automated driver management).

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