Add test.

tests/integration/test_create_user_and_login/test.py

@@ -1,5 +1,8 @@
 import pytest
+import time
+import logging
 from helpers.cluster import ClickHouseCluster
+from helpers.test_tools import assert_eq_with_retry
 
 cluster = ClickHouseCluster(__file__)
 instance = cluster.add_instance('instance')
@@ -38,3 +41,46 @@ def test_grant_create_user():
     instance.query("GRANT CREATE USER ON *.* TO A")
     instance.query("CREATE USER B", user='A')
     assert instance.query("SELECT 1", user='B') == "1\n"
+
+
+def test_login_as_dropped_user():
+    for _ in range(0, 2):
+        instance.query("CREATE USER A")
+        assert instance.query("SELECT 1", user='A') == "1\n"
+
+        instance.query("DROP USER A")
+        expected_error = "no user with such name"
+        assert expected_error in instance.query_and_get_error("SELECT 1", user='A')
+
+
+def test_login_as_dropped_user_xml():
+    for _ in range(0, 2):
+        instance.exec_in_container(["bash", "-c" , """
+            cat > /etc/clickhouse-server/users.d/user_c.xml << EOF
+<?xml version="1.0"?>
+<yandex>
+    <users>
+        <C>
+            <no_password/>
+        </C>
+    </users>
+</yandex>
+EOF"""])
+
+        assert_eq_with_retry(instance, "SELECT name FROM system.users WHERE name='C'", "C")
+
+        instance.exec_in_container(["bash", "-c" , "rm /etc/clickhouse-server/users.d/user_c.xml"])
+
+        expected_error = "no user with such name"
+        while True:
+            out, err = instance.query_and_get_answer_with_error("SELECT 1", user='C')
+            if expected_error in err:
+                logging.debug(f"Got error '{expected_error}' just as expected")
+                break
+            if out == "1\n":
+                logging.debug(f"Got output '1', retrying...")
+                time.sleep(0.5)
+                continue
+            raise Exception(f"Expected either output '1' or error '{expected_error}', got output={out} and error={err}")
+            
+        assert instance.query("SELECT name FROM system.users WHERE name='C'") == ""