Django Unittest fails when run parallel on CircleCI - mysql

Question

I am running Django Unit tests on CircleCI with 1 container setup. The tests run fine when I do not add Django's --parallel argument. However, when I add --parallel=2 to the test run, it fails with this cryptic error below.
I've tried both versions: with and without --keepdb - both fail with exactly the same error. The code for _clode_test_db appears to suggest that passing --keepdb=True should fail fast and return. See django/db/backends/mysql/creation.py line: 29 here [https://github.com/django/django/pull/4761/files]
Would appreciate any ideas on what is going on here
Using existing clone for alias 'default' ('test_django_learned')...
Traceback (most recent call last):
File "manage.py", line 10, in <module>
execute_from_command_line(sys.argv)
File "/home/circleci/sliderule/venv/lib/python2.7/site-packages/django/core/management/__init__.py", line 353, in execute_from_command_line
utility.execute()
File "/home/circleci/sliderule/venv/lib/python2.7/site-packages/django/core/management/__init__.py", line 345, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "/home/circleci/sliderule/venv/lib/python2.7/site-packages/django/core/management/commands/test.py", line 30, in run_from_argv
super(Command, self).run_from_argv(argv)
File "/home/circleci/sliderule/venv/lib/python2.7/site-packages/django/core/management/base.py", line 348, in run_from_argv
self.execute(*args, **cmd_options)
File "/home/circleci/sliderule/venv/lib/python2.7/site-packages/django/core/management/commands/test.py", line 74, in execute
super(Command, self).execute(*args, **options)
File "/home/circleci/sliderule/venv/lib/python2.7/site-packages/django/core/management/base.py", line 399, in execute
output = self.handle(*args, **options)
File "/home/circleci/sliderule/venv/lib/python2.7/site-packages/django/core/management/commands/test.py", line 90, in handle
failures = test_runner.run_tests(test_labels)
File "/home/circleci/sliderule/venv/lib/python2.7/site-packages/django/test/runner.py", line 532, in run_tests
old_config = self.setup_databases()
File "/home/circleci/sliderule/venv/lib/python2.7/site-packages/django/test/runner.py", line 482, in setup_databases
self.parallel, **kwargs
File "/home/circleci/sliderule/venv/lib/python2.7/site-packages/django/test/runner.py", line 733, in setup_databases
keepdb=keepdb,
File "/home/circleci/sliderule/venv/lib/python2.7/site-packages/django/db/backends/base/creation.py", line 219, in clone_test_db
self._clone_test_db(number, verbosity, keepdb)
File "/home/circleci/sliderule/venv/lib/python2.7/site-packages/django/db/backends/mysql/creation.py", line 48, in _clone_test_db
dump_proc = subprocess.Popen(dump_cmd, stdout=subprocess.PIPE)
File "/usr/local/lib/python2.7/subprocess.py", line 390, in __init__
errread, errwrite)
File "/usr/local/lib/python2.7/subprocess.py", line 1024, in _execute_child
raise child_exception
OSError: [Errno 2] No such file or directory
Exited with code 1

Answer 1

I could reproduce it and debugged the problem in my ubuntu container by adding
sys.stderr.write("dump_cmd: %r" % dump_cmd)
to site-packages/django/db/backends/mysql/creation.py and it gave me
dump_cmd: ['mysqldump', '--user=root', '--password=pass', '--host=db', '--port=3306', 'test']
So probably your container is also missing mysqldump which I fixed with a simple sudo apt-get install mysql-client.