Speed up execution of thermalctld unit tests

[aditya-nexthop]

Description

Replace the real swsssdk imports in mocked_libs/swsscommon/swsscommon.py with mock stubs for ConfigDBConnector and SonicV2Connector, eliminating all swsssdk dependencies from the test environment, and add the missing getKeys() method to mock_swsscommon.Table.

Motivation and Context

The thermalctld test suite was taking ~36 minutes to run due to Redis connection timeouts incurred on every TemperatureUpdater construction.

TemperatureUpdater.__init__ calls _init_sfp_util_helper(), which invokes SfpUtilHelper().read_porttab_mappings(). This triggers up to 7 calls to device_info.get_localhost_info() per construction through three call chains: get_platform_and_hwsku(), get_port_config(), and get_path_to_port_config_file(). Each call creates a ConfigDBConnector (from swsscommon.swsscommon) that retries connecting to Redis ~3 times with ~7s sleep per retry.

The root cause is that mocked_libs/swsscommon/swsscommon.py was re-exporting the real ConfigDBConnector and SonicV2Connector from swsssdk instead of providing mock stubs. Since device_info.py imports these via from swsscommon.swsscommon import ConfigDBConnector, SonicV2Connector, and the mocked package is first in sys.path during tests, replacing them with no-op stubs is sufficient to prevent all Redis connection attempts with no other test changes required.

mock_swsscommon.Table was also missing getKeys(), which TemperatureUpdater.__del__ calls during cleanup, causing an AttributeError warning on every test that constructs a TemperatureUpdater.

How Has This Been Tested?

Profiled test_dpu_chassis_thermals (the worst offender) using cProfile:

28880 function calls in 49.403 seconds

device_info.get_localhost_info   7 calls × 7.057s = 49.4s total
  └─ swsssdk ConfigDBConnector.connect
     └─ redis retry: 21 × time.sleep(2.35s) = 49.4s

After fix:

• test_dpu_chassis_thermals: ~230s → 0.07s
• Full suite: ~36 minutes → ~1 minute

Additional Information (Optional)

The mock stubs follow the same pattern used in sonic-chassisd/tests/mock_swsscommon.py.

SonicV2Connector is stubbed alongside ConfigDBConnector because device_info.py imports both in a single statement (from swsscommon.swsscommon import ConfigDBConnector, SonicV2Connector). swsssdk conditionally bypasses its own deprecation ImportError when mock or unittest are already in sys.modules — so during pytest the real SonicV2Connector would be importable. Stubbing it explicitly removes the dependency on this behavior and ensures swsssdk is never imported in the test environment.

fixes #788

[mssonicbld]

/azp run

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[mssonicbld]

/azp run

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[mssonicbld]

/azp run

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[aditya-nexthop]

@judyjoseph please can you take a look at this PR?

[vvolam]

LGTM, Thanks!