[watermarkstat] Add new warning message for the 'q_shared_multi' counters (sonic-net#2408)

- What I did
Add a new warning message for the 'q_shared_multi' counter and not perform the exit with error code (1) because of the new implementation sonic-swss/pull/2432 from now on there is a valid case if there are no multicast counters inside the COUNTERS_DB.

In order for multicast counters to be presented in COUNTERS_DB the appropriate queues should be configured inside the CONFIG_DB (e.g "BUFFER_QUEUE|Ethernet14|7-8")

- How I did it
Change the watermarkstat script

- How to verify it
Run the sonic-mgmt/tests/iface_namingmode/test_iface_namingmode.py

Previous command output (if the output of a command-line utility has changed)
root@sonic:/home/admin# show queue watermark multicast
Object map is empty!

New command output (if the output of a command-line utility has changed)
root@sonic:/home/admin# show queue watermark multicast
Object map from the COUNTERS_DB is empty because the multicast queues are not configured in the CONFIG_DB!

Author: vadymhlushko-mlnx

scripts/watermarkstat

@@ -21,8 +21,16 @@ try:
         tests_path = os.path.join(modules_path, "tests")
         sys.path.insert(0, modules_path)
         sys.path.insert(0, tests_path)
-        import mock_tables.dbconnector
+        from mock_tables import dbconnector
 
+        if os.environ["WATERMARKSTAT_UNIT_TESTING"] == "1":
+            input_path = os.path.join(tests_path, "wm_input")
+            mock_db_path = os.path.join(input_path, "mock_db")
+
+            for mock_db in os.listdir(mock_db_path):
+                name, ext = os.path.splitext(mock_db)
+                if ext == ".json":
+                    dbconnector.dedicated_dbs[name.upper()] = os.path.join(mock_db_path, name)
 except KeyError:
     pass
 
@@ -201,7 +209,7 @@ class Watermarkstat(object):
 
         return pg_index
 
-    def build_header(self, wm_type):
+    def build_header(self, wm_type, counter_type):
         if wm_type is None:
             print("Header info is not available!", file=sys.stderr)
             sys.exit(1)
@@ -220,8 +228,12 @@ class Watermarkstat(object):
                     min_idx = element_idx
 
         if min_idx == sys.maxsize:
-            print("Object map is empty!", file=sys.stderr)
-            sys.exit(1)
+            if counter_type != 'q_shared_multi':
+                print("Object map is empty!", file=sys.stderr)
+                sys.exit(1)
+            else:
+                print("Object map from the COUNTERS_DB is empty because the multicast queues are not configured in the CONFIG_DB!")
+                sys.exit(0)
 
         self.min_idx = min_idx
         self.header_list += ["{}{}".format(wm_type["header_prefix"], idx) for idx in range(self.min_idx, max_idx + 1)]
@@ -264,7 +276,7 @@ class Watermarkstat(object):
                     data = STATUS_NA
                 table.append((buf_pool, data))
         else:
-            self.build_header(type)
+            self.build_header(type, key)
             # Get stat for each port
             for port in natsorted(self.counter_port_name_map):
                 row_data = list()

tests/watermarkstat_test.py

@@ -1,5 +1,6 @@
 import os
 import sys
+import pytest
 
 import show.main as show
 from click.testing import CliRunner
@@ -13,6 +14,15 @@
 sys.path.insert(0, modules_path)
 
 
+@pytest.fixture(scope="function")
+def q_multicast_wm_neg():
+    print("Setup watermarkstat sample data: no queue multicast watermark counters")
+    os.environ['WATERMARKSTAT_UNIT_TESTING'] = "1"
+    yield
+    del os.environ['WATERMARKSTAT_UNIT_TESTING']
+    print("Teardown watermarkstat sample data: no queue multicast watermark counters")
+
+
 class TestWatermarkstat(object):
     @classmethod
     def setup_class(cls):
@@ -32,6 +42,9 @@ def test_show_queue_unicast_wm(self):
     def test_show_queue_multicast_wm(self):
         self.executor(testData['show_q_wm_multicast'])
 
+    def test_show_queue_multicast_wm_neg(self, q_multicast_wm_neg):
+        self.executor(testData['show_q_wm_multicast_neg'])
+
     def test_show_queue_all_wm(self):
         self.executor(testData['show_q_wm_all'])