[acl] Make Config DB recovery more robust

tests/acl/test_acl.py

@@ -14,6 +14,7 @@
 
 from tests.common import reboot, port_toggle
 from tests.common.plugins.loganalyzer.loganalyzer import LogAnalyzer, LogAnalyzerError
+from tests.common.fixtures.duthost_utils import backup_and_restore_config_db_module
 
 logger = logging.getLogger(__name__)
 
@@ -189,8 +190,8 @@ def acl_table_config(duthost, setup, stage):
     }
 
 
-@pytest.fixture(scope='module')
-def acl_table(duthost, acl_table_config):
+@pytest.fixture(scope="module")
+def acl_table(duthost, acl_table_config, backup_and_restore_config_db_module):
     """
     fixture to apply ACL table configuration and remove after tests
     :param duthost: DUT object
@@ -223,9 +224,6 @@ def acl_table(duthost, acl_table_config):
             logger.info('removing ACL table {}'.format(name))
             duthost.command('config acl remove table {}'.format(name))
 
-        # save cleaned configuration
-        duthost.command('config save -y')
-
 
 class BaseAclTest(object):
     """

tests/common/fixtures/duthost_utils.py

@@ -3,17 +3,36 @@
 
 logger = logging.getLogger(__name__)
 
-@pytest.fixture
-def backup_and_restore_config_db(duthost):
-    """
-    Some cases will shutdown interfaces or BGP in test, and the change is writen to
-    config db after warm-reboot. Therefore, we need to backup config_db.json before
-    test starts and then restore after test ends
+
+def _backup_and_restore_config_db(duthost):
+    """Back up the existing config_db.json file and restore it once the test ends.
+
+    Some cases will update the running config during the test and save the config
+    to be recovered aftet reboot. In such a case we need to backup config_db.json before
+    the test starts and then restore it after the test ends.
     """
     CONFIG_DB = "/etc/sonic/config_db.json"
     CONFIG_DB_BAK = "/etc/sonic/config_db.json.before_test"
     logger.info("Backup {} to {}".format(CONFIG_DB, CONFIG_DB_BAK))
     duthost.shell("cp {} {}".format(CONFIG_DB, CONFIG_DB_BAK))
+
     yield
+
     logger.info("Restore {} with {}".format(CONFIG_DB, CONFIG_DB_BAK))
     duthost.shell("mv {} {}".format(CONFIG_DB_BAK, CONFIG_DB))
+
+
+@pytest.fixture
+def backup_and_restore_config_db(duthost):
+    """Back up and restore config DB at the function level."""
+    # TODO: Use the neater "yield from _function" syntax when we move to python3
+    for func in _backup_and_restore_config_db(duthost):
+        yield func
+
+
+@pytest.fixture(scope="module")
+def backup_and_restore_config_db_module(duthost):
+    """Back up and restore config DB at the module level."""
+    # TODO: Use the neater "yield from _function" syntax when we move to python3
+    for func in _backup_and_restore_config_db(duthost):
+        yield func