sonic-mgmt: Add FEC check test case. (sonic-net#12397)

* Add test_intf_fec.py

* Add more supported platforms and fix the indentation

* Add more information on Cisco platforms

* Fix a trailing whitespace

* Address review comment.

Add a check for speed and sfp presence as well.

* Add config FEC test

* Use "show interfaces fec status" command to retrieve FEC operational mode

tests/platform_tests/test_intf_fec.py

@@ -0,0 +1,93 @@
+import logging
+import pytest
+
+from tests.common.utilities import skip_release
+
+pytestmark = [
+    pytest.mark.disable_loganalyzer,  # disable automatic loganalyzer
+    pytest.mark.topology('any')
+]
+
+SUPPORTED_PLATFORMS = [
+    "mlnx_msn",
+    "8101_32fh",
+    "8111_32eh"
+]
+
+SUPPORTED_SPEEDS = [
+    "100G", "200G", "400G", "800G", "1600G"
+]
+
+
+def test_verify_fec_oper_mode(duthosts, enum_rand_one_per_hwsku_frontend_hostname,
+                              enum_frontend_asic_index, conn_graph_facts):
+    """
+    @Summary: Verify the FEC operational mode is valid, for all the interfaces with
+    SFP present, supported speeds and link is up using 'show interface status'
+    """
+    duthost = duthosts[enum_rand_one_per_hwsku_frontend_hostname]
+
+    if any(platform in duthost.facts['platform'] for platform in SUPPORTED_PLATFORMS):
+        # Not supported on 202305 and older releases
+        skip_release(duthost, ["201811", "201911", "202012", "202205", "202211", "202305"])
+    else:
+        pytest.skip("DUT has platform {}, test is not supported".format(duthost.facts['platform']))
+
+    logging.info("Get output of '{}'".format("show interface status"))
+    intf_status = duthost.show_and_parse("show interface status")
+
+    for intf in intf_status:
+        sfp_presence = duthost.show_and_parse("sudo sfpshow presence -p {}"
+                                              .format(intf['interface']))
+        if sfp_presence:
+            presence = sfp_presence[0].get('presence', '').lower()
+            oper = intf.get('oper', '').lower()
+            speed = intf.get('speed', '')
+
+            if presence == "present" and oper == "up" and speed in SUPPORTED_SPEEDS:
+                # Verify the FEC operational mode is valid
+                logging.info("Get output of '{} {}'".format("show interfaces fec status", intf['interface']))
+                fec_status = duthost.show_and_parse("show interfaces fec status {}".format(intf['interface']))
+                fec = fec_status[0].get('fec oper', '').lower()
+                if fec == "n/a":
+                    pytest.fail("FEC status is N/A for interface {}".format(intf['interface']))
+
+
+def test_config_fec_oper_mode(duthosts, enum_rand_one_per_hwsku_frontend_hostname,
+                              enum_frontend_asic_index, conn_graph_facts):
+    """
+    @Summary: Configure the FEC operational mode for all the interfaces, then check
+    FEC operational mode is retored to default FEC mode
+    """
+    duthost = duthosts[enum_rand_one_per_hwsku_frontend_hostname]
+
+    if any(platform in duthost.facts['platform'] for platform in SUPPORTED_PLATFORMS):
+        # Not supported on 202305 and older releases
+        skip_release(duthost, ["201811", "201911", "202012", "202205", "202211", "202305"])
+    else:
+        pytest.skip("DUT has platform {}, test is not supported".format(duthost.facts['platform']))
+
+    logging.info("Get output of '{}'".format("show interface status"))
+    intf_status = duthost.show_and_parse("show interface status")
+
+    for intf in intf_status:
+        sfp_presence = duthost.show_and_parse("sudo sfpshow presence -p {}"
+                                              .format(intf['interface']))
+        if sfp_presence:
+            presence = sfp_presence[0].get('presence', '').lower()
+            oper = intf.get('oper', '').lower()
+
+            if presence == "not present" or oper != "up":
+                continue
+
+        config_status = duthost.command("sudo config interface fec {} rs"
+                                        .format(intf['interface']))
+        if config_status:
+            duthost.command("sleep 2")
+            # Verify the FEC operational mode is restored
+            logging.info("Get output of '{} {}'".format("show interfaces fec status", intf['interface']))
+            fec_status = duthost.show_and_parse("show interfaces fec status {}".format(intf['interface']))
+            fec = fec_status[0].get('fec oper', '').lower()
+
+            if not (fec == "rs"):
+                pytest.fail("FEC status is not restored for interface {}".format(intf['interface']))