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In an Django application that I freshly created, where I changed it to use PostgreSQL and I created one app, I have the following test:

from django.contrib.auth.models import User
from django.contrib.staticfiles.testing import StaticLiveServerTestCase
from selenium import webdriver
from selenium.webdriver.common.keys import Keys


class TestWebBrowser(StaticLiveServerTestCase):
 @classmethod
 def setUpClass(cls):
 super().setUpClass()
 cls.webdriver = webdriver.Chrome()
 cls.webdriver.implicitly_wait(10)

 @classmethod
 def tearDownClass(cls):
 cls.webdriver.close()
 cls.webdriver.quit()
 super().tearDownClass()

 def setUp(self):
 self.admin = User.objects.create_superuser(username="username", password="password",
 email="example@example.com")

 def test_log_in(self):
 self.webdriver.get(f"self.live_server_url/admin")
 self.webdriver.find_element_by_id("id_username").send_keys("username")
 self.webdriver.find_element_by_id("id_password").send_keys("password")
 self.webdriver.find_element_by_id("id_password").send_keys(Keys.RETURN)
 self.webdriver.find_element_by_link_text("Users").click()

The test always runs, Chrome starts, does what the test say, but at the end, sometimes it throws this error:

Exception happened during processing of request from ('127.0.0.1', 55283)
Traceback (most recent call last):
 File "C:Userspupenoscoopappspythoncurrentlibsocketserver.py", line 647, in process_request_thread
 self.finish_request(request, client_address)
 File "C:Userspupenoscoopappspythoncurrentlibsocketserver.py", line 357, in finish_request
 self.RequestHandlerClass(request, client_address, self)
 File "C:Userspupenoscoopappspythoncurrentlibsocketserver.py", line 717, in __init__
 self.handle()
 File "C:UserspupenoTemporaryuntitledvenvlibsite-packagesdjangocoreserversbasehttp.py", line 139, in handle
 self.raw_requestline = self.rfile.readline(65537)
 File "C:Userspupenoscoopappspythoncurrentlibsocket.py", line 589, in readinto
 return self._sock.recv_into(b)
ConnectionResetError: [WinError 10054] An existing connection was forcibly closed by the remote host

All tests pass. I just get that to STDERR. Any ideas why? Am I missing some tearing-down?

If I change tearDownClass to:

@classmethod
def tearDownClass(cls):
 cls.webdriver.quit()

I get the same error with the same frequency (as far as I can observe, without having measured it).

I'm running:

Django==2.1.2
selenium==3.141.0

and

> chromedriver.exe --version
ChromeDriver 2.43.600210 (68dcf5eebde37173d4027fa8635e332711d2874a)

and

Google Chrome Version 70.0.3538.102 (Official Build) (64-bit)

The full output of running the tests look like this:

Testing started at 15:33 ...
C:UserspupenoTemporaryuntitledvenvScriptspython.exe "C:Program FilesJetBrainsPyCharm 2018.2.4helperspycharmdjango_test_manage.py" test foo.tests.TestImportCRMData C:UserspupenoTemporaryuntitled
Creating test database for alias 'default'...
System check identified no issues (0 silenced).
----------------------------------------
Exception happened during processing of request from ('127.0.0.1', 49825)
Traceback (most recent call last):
 File "C:Userspupenoscoopappspythoncurrentlibsocketserver.py", line 647, in process_request_thread
 self.finish_request(request, client_address)
 File "C:Userspupenoscoopappspythoncurrentlibsocketserver.py", line 357, in finish_request
 self.RequestHandlerClass(request, client_address, self)
 File "C:Userspupenoscoopappspythoncurrentlibsocketserver.py", line 717, in __init__
 self.handle()
 File "C:UserspupenoTemporaryuntitledvenvlibsite-packagesdjangocoreserversbasehttp.py", line 139, in handle
 self.raw_requestline = self.rfile.readline(65537)
 File "C:Userspupenoscoopappspythoncurrentlibsocket.py", line 589, in readinto
 return self._sock.recv_into(b)
ConnectionResetError: [WinError 10054] An existing connection was forcibly closed by the remote host
----------------------------------------
Destroying test database for alias 'default'...

Process finished with exit code 0

This error message...

ConnectionResetError: [WinError 10054] An existing connection was forcibly closed by the remote host

...implies that the ChromeDriver was unable to communicate with the WebBrowsing Session i.e. Chrome Browser session as it was forcibly closed by the remote host.

Your main issue is the multiple calls in the form of webdriver.close() and webdriver.quit()

While automating through Selenium as per the best practices to terminate a connection you should always invoke driver.quit() within tearDown() method to close & destroy the WebDriver and Web Client instances gracefully. Invoking quit() method DELETEs the current browsing session through sending "quit" command with "flags":["eForceQuit"] and finally sends the GET request on /shutdown EndPoint. Here is an example below :

1503397488598 webdriver::server DEBUG -> DELETE /session/8e457516-3335-4d3b-9140-53fb52aa8b74 
1503397488607 geckodriver::marionette TRACE -> 37:[0,4,"quit","flags":["eForceQuit"]]
1503397488821 webdriver::server DEBUG -> GET /shutdown

So on invoking quit() method the Web Browser session and the WebDriver instance gets killed completely. Hence you don't have to incorporate any additional steps (invoking close()) which will be an overhead by the prevailing standards.

Solution

First of all you remove the following line:

cls.webdriver.close()

The very next line:

cls.webdriver.quit()

Is bound to terminate the connection in the best possible way.

Here you can find a detailed discussion on Selenium : How to stop geckodriver process impacting PC memory, without calling driver.quit()?

Update A

As per the liveservertestcase the tearDownClass() @classmethod isdefined as:

@classmethod
def tearDownClass(cls):
 cls.selenium.quit()
 super().tearDownClass()

As per django/django/test/testcases.py this is called:

@classmethod
def tearDownClass(cls):
 cls._tearDownClassInternal()
 cls._live_server_modified_settings.disable()
 super().tearDownClass()