Provide BMC defaults for system status LED methods in ChassisBase (#731)

* Provide BMC defaults for system status LED methods in ChassisBase

`show system-health` (sonic-utilities) calls initizalize_system_led(),
set_status_led() and get_status_led() unconditionally on the chassis, but
BMC platforms have no controllable system status LED. ChassisBase left
set/get as NotImplementedError and had no initizalize_system_led at all,
so the CLI failed on BMC images.

Provide BMC defaults in ChassisBase, gated on is_switch_bmc():
initizalize_system_led() returns True, set_status_led() returns False, and
get_status_led() returns "N/A". Non-BMC platforms are unaffected: they fall
through to NotImplementedError as before, or override these methods.

Signed-off-by: shreyansh-nexthop <shreyansh@nexthop.ai>

* Add unit tests for the ChassisBase system LED BMC defaults

Cover both branches of initizalize_system_led(), set_status_led() and
get_status_led(): the BMC defaults when is_switch_bmc() is true, and the
NotImplementedError path for non-BMC platforms.

Signed-off-by: shreyansh-nexthop <shreyansh@nexthop.ai>

---------

Signed-off-by: shreyansh-nexthop <shreyansh@nexthop.ai>

Author: shreyansh-nexthop

sonic_platform_base/chassis_base.py

@@ -884,6 +884,18 @@ def get_port_or_cage_type(self, index):
     # System LED methods
     ##############################################
 
+    def initizalize_system_led(self):
+        """
+        Initialize the system status LED.
+
+        Returns:
+            bool: True if the system LED was initialized successfully.
+        """
+        if device_info and device_info.is_switch_bmc():
+            # BMC platforms have no controllable system LED, nothing to initialize.
+            return True
+        raise NotImplementedError
+
     def set_status_led(self, color):
         """
         Sets the state of the system LED
@@ -895,6 +907,9 @@ def set_status_led(self, color):
         Returns:
             bool: True if system LED state is set successfully, False if not
         """
+        if device_info and device_info.is_switch_bmc():
+            # BMC platforms have no controllable system LED.
+            return False
         raise NotImplementedError
 
     def get_status_led(self):
@@ -905,6 +920,9 @@ def get_status_led(self):
             A string, one of the valid LED color strings which could be vendor
             specified.
         """
+        if device_info and device_info.is_switch_bmc():
+            # BMC platforms have no controllable system LED.
+            return "N/A"
         raise NotImplementedError
 
     ##############################################

tests/chassis_base_test.py

@@ -58,6 +58,61 @@ def test_chassis_base(self):
 
             assert exception_raised
 
+    @mock.patch('sonic_py_common.device_info.is_switch_bmc', return_value=True)
+    def test_system_led_bmc(self, _mock_is_switch_bmc):
+        # BMC platforms have no controllable system LED, so the base class
+        # provides no-op defaults instead of raising NotImplementedError.
+        chassis = ChassisBase()
+        assert(chassis.initizalize_system_led() == True)
+        assert(chassis.set_status_led("green") == False)
+        assert(chassis.get_status_led() == "N/A")
+
+    @mock.patch.object(chassis_base, 'device_info', None)
+    def test_system_led_no_device_info(self):
+        # chassis_base tolerates device_info being None when sonic_py_common is
+        # shadowed by a partial mock. These methods must still raise
+        # NotImplementedError rather than AttributeError in that case.
+        chassis = ChassisBase()
+        not_implemented_methods = [
+                [chassis.initizalize_system_led, [], {}],
+                [chassis.set_status_led, ["COLOR"], {}],
+                [chassis.get_status_led, [], {}],
+            ]
+
+        for method in not_implemented_methods:
+            exception_raised = False
+            try:
+                func = method[0]
+                args = method[1]
+                kwargs = method[2]
+                func(*args, **kwargs)
+            except NotImplementedError:
+                exception_raised = True
+
+            assert exception_raised
+
+    @mock.patch('sonic_py_common.device_info.is_switch_bmc', return_value=False)
+    def test_system_led_non_bmc(self, _mock_is_switch_bmc):
+        # Non-BMC platforms are expected to implement these themselves.
+        chassis = ChassisBase()
+        not_implemented_methods = [
+                [chassis.initizalize_system_led, [], {}],
+                [chassis.set_status_led, ["COLOR"], {}],
+                [chassis.get_status_led, [], {}],
+            ]
+
+        for method in not_implemented_methods:
+            exception_raised = False
+            try:
+                func = method[0]
+                args = method[1]
+                kwargs = method[2]
+                func(*args, **kwargs)
+            except NotImplementedError:
+                exception_raised = True
+
+            assert exception_raised
+
     def test_smartswitch(self):
         chassis = ChassisBase()
         assert(chassis.is_smartswitch() == False)