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BRIEF DESCRIPTION OF THE PROBLEM: Psycopg2 won't connect to a test DB within docker from unittest, but connects fine from console.

ERROR MESSAGE:
psycopg2.OperationalError: server closed the connection unexpectedly
This probably means the server terminated abnormally before or while processing the request.

DETAILS:
I'm trying to set up a testing database in docker, that will be created and populated before testing and then removed after.

Here's the fuction to set up database:

def set_up_empty_test_db():
 client = docker.from_env()
 try:
 testdb = client.containers.get("TestDB")
 testdb.stop()
 testdb.remove()
 testdb = client.containers.run(
 "postgres",
 ports=5432: 5433,
 detach=True,
 name="TestDB",
 environment=["POSTGRES_PASSWORD=yourPassword"],
 )
 except NotFound:
 testdb = client.containers.run(
 "postgres",
 ports=5432: 5433,
 detach=True,
 name="TestDB",
 environment=["POSTGRES_PASSWORD=yourPassword"],
 )

 while testdb.status != "running":
 testdb = client.containers.get("TestDB")
 return 

If I launch this function from console it works without an error and I can see TestDB container running. I can successfully initiate connection:

conn = psycopg2.connect("host='localhost' user='postgres' password='yourPassword' port='5433'")

But it doesn't work when unit testing. Here's the testing code:

class TestCreateCity(unittest.TestCase):
 def setUp(self):
 set_up_empty_test_db()
 con = psycopg2.connect("host='localhost' user='postgres' password='yourPassword' port='5433'")

 self.assertIsNone(con.isolation_level)

 cur = con.cursor()
 sql_file = open(os.path.join(ROOT_DIR + "/ddl/creates/schema_y.sql"), "r")
 cur.execute(sql_file.readline())
 con.commit()
 con.close()
 self.session = Session(creator=con)

 def test_create_city(self):
 cs.create_city("Test_CITY", "US")
 q = self.session.query(City).filter(City.city_name == "Test_CITY").one()
 self.assertIs(q)
 self.assertEqual(q.city_name, "Test_CITY")
 self.assertEqual(q.country_code, "US")

It breaks when trying to initiate connection. Please advise.

I know this is an old question, but I needed to do the same thing today. You try and connect to the postgres server too quickly after starting it - that's why it works in the console.

All you need to do is replace:

set_up_empty_test_db()
con = psycopg2.connect("host='localhost' user='postgres' password='yourPassword' port='5433'")

with:

set_up_empty_test_db()
con = None
while con == None:
 try:
 con = psycopg2.connect("host='localhost' user='postgres' password='yourPassword' port='5433'")
 except psycopg2.OperationalError:
 time.sleep(0.5);

Hope this helps someone else. Cheers!