[psud] Increase unit test coverage (sonic-net#140)

- Add 100% unit test coverage of `PsuStatus` class in psud.
- Add skeleton of class to test `DaemonPsud` class
- Add test case for `get_psu_key()` and `try_get()` helper functions
- Add checks to import 'mock' from the 'unittest' package if running with Python 3

Overall psud unit test coverage increases from 39% to 51%.

Previous unit test coverage:

```
----------- coverage: platform linux, python 3.7.3-final-0 -----------
Name           Stmts   Miss  Cover
----------------------------------
scripts/psud     381    233    39%
Coverage HTML written to dir htmlcov
Coverage XML written to file coverage.xml
```

Unit test coverage with this patch:

```
----------- coverage: platform linux, python 3.7.3-final-0 -----------
Name           Stmts   Miss  Cover
----------------------------------
scripts/psud     381    185    51%
Coverage HTML written to dir htmlcov
Coverage XML written to file coverage.xml
```

sonic-psud/setup.py

@@ -21,8 +21,8 @@
         'wheel'
     ],
     tests_require=[
+        'mock>=2.0.0; python_version < "3.3"',
         'pytest',
-        'mock>=2.0.0',
         'pytest-cov'
     ],
     classifiers=[

sonic-psud/tests/mock_platform.py

@@ -37,10 +37,18 @@ def __init__(self, psu_presence, psu_status, psu_name):
         self.name = psu_name
         self.presence = True
         self.psu_status = psu_status
+        self.status_led_color = self.STATUS_LED_COLOR_OFF
 
     def get_powergood_status(self):
         return self.psu_status
 
+    def set_status_led(self, color):
+        self.status_led_color = color
+        return True
+
+    def get_status_led(self):
+        return self.status_led_color
+
     def set_status(self, status):
         self.psu_status = status
 

sonic-psud/tests/test_PsuStatus.py

@@ -0,0 +1,236 @@
+import os
+import sys
+from imp import load_source
+
+# TODO: Clean this up once we no longer need to support Python 2
+if sys.version_info.major == 3:
+    from unittest.mock import MagicMock
+else:
+    from mock import MagicMock
+
+from .mock_platform import MockPsu
+
+test_path = os.path.dirname(os.path.abspath(__file__))
+modules_path = os.path.dirname(test_path)
+scripts_path = os.path.join(modules_path, "scripts")
+sys.path.insert(0, modules_path)
+
+os.environ["PSUD_UNIT_TESTING"] = "1"
+load_source('psud', scripts_path + '/psud')
+from psud import *
+
+
+class TestPsuStatus(object):
+    """
+    Test cases to cover functionality of PsuStatus class
+    """
+
+    def test_set_presence(self):
+        mock_logger = MagicMock()
+        mock_psu = MockPsu(True, True, "PSU 1")
+
+        psu_status = PsuStatus(mock_logger, mock_psu)
+        assert psu_status.presence == False
+
+        # Test toggling presence to True
+        ret = psu_status.set_presence(True)
+        assert ret == True
+        assert psu_status.presence == True
+
+        # Test toggling presence to False
+        ret = psu_status.set_presence(False)
+        assert ret == True
+        assert psu_status.presence == False
+
+        # Test attempting to set presence to the same as the current value
+        ret = psu_status.set_presence(False)
+        assert ret == False
+        assert psu_status.presence == False
+
+    def test_set_power_good(self):
+        mock_logger = MagicMock()
+        mock_psu = MockPsu(True, True, "PSU 1")
+
+        psu_status = PsuStatus(mock_logger, mock_psu)
+        assert psu_status.power_good == False
+
+        # Test toggling power_good to True
+        ret = psu_status.set_power_good(True)
+        assert ret == True
+        assert psu_status.power_good == True
+
+        # Test attempting to set power_good to the same as the current value (return value should be False)
+        ret = psu_status.set_power_good(True)
+        assert ret == False
+        assert psu_status.power_good == True
+
+        # Test toggling power_good to False
+        ret = psu_status.set_power_good(False)
+        assert ret == True
+        assert psu_status.power_good == False
+
+        # Test attempting to set power_good to the same as the current value (return value should be False)
+        ret = psu_status.set_power_good(False)
+        assert ret == False
+        assert psu_status.power_good == False
+
+    def test_set_voltage(self):
+        mock_logger = MagicMock()
+        mock_psu = MockPsu(True, True, "PSU 1")
+
+        psu_status = PsuStatus(mock_logger, mock_psu)
+        assert psu_status.voltage_good == False
+
+        # Pass in a good voltage
+        ret = psu_status.set_voltage(12.0, 12.5, 11.5)
+        assert ret == True
+        assert psu_status.voltage_good == True
+
+        # Pass in a another good voltage successively (return value should be False)
+        ret = psu_status.set_voltage(11.9, 12.5, 11.5)
+        assert ret == False
+        assert psu_status.voltage_good == True
+
+        # Pass in a high voltage
+        ret = psu_status.set_voltage(12.6, 12.5, 11.5)
+        assert ret == True
+        assert psu_status.voltage_good == False
+
+        # Pass in a another bad voltage successively (return value should be False)
+        ret = psu_status.set_voltage(12.7, 12.5, 11.5)
+        assert ret == False
+        assert psu_status.voltage_good == False
+
+        # Pass in a good (high edge case) voltage
+        ret = psu_status.set_voltage(12.5, 12.5, 11.5)
+        assert ret == True
+        assert psu_status.voltage_good == True
+
+        # Pass in a low voltage
+        ret = psu_status.set_voltage(11.4, 12.5, 11.5)
+        assert ret == True
+        assert psu_status.voltage_good == False
+
+        # Pass in a good (low edge case) voltage
+        ret = psu_status.set_voltage(11.5, 12.5, 11.5)
+        assert ret == True
+        assert psu_status.voltage_good == True
+
+        # Test passing parameters as None when voltage_good == True
+        ret = psu_status.set_voltage(None, 12.5, 11.5)
+        assert ret == False
+        assert psu_status.voltage_good == True
+        ret = psu_status.set_voltage(11.5, None, 11.5)
+        assert ret == False
+        assert psu_status.voltage_good == True
+        ret = psu_status.set_voltage(11.5, 12.5, None)
+        assert ret == False
+        assert psu_status.voltage_good == True
+
+        # Test passing parameters as None when voltage_good == False
+        psu_status.voltage_good = False
+        ret = psu_status.set_voltage(None, 12.5, 11.5)
+        assert ret == False
+        assert psu_status.voltage_good == True
+        psu_status.voltage_good = False
+        ret = psu_status.set_voltage(11.5, None, 11.5)
+        assert ret == False
+        assert psu_status.voltage_good == True
+        psu_status.voltage_good = False
+        ret = psu_status.set_voltage(11.5, 12.5, None)
+        assert ret == False
+        assert psu_status.voltage_good == True
+
+    def test_set_temperature(self):
+        mock_logger = MagicMock()
+        mock_psu = MockPsu(True, True, "PSU 1")
+
+        psu_status = PsuStatus(mock_logger, mock_psu)
+        assert psu_status.temperature_good == False
+
+        # Pass in a good temperature
+        ret = psu_status.set_temperature(20.123, 50.0)
+        assert ret == True
+        assert psu_status.temperature_good == True
+
+        # Pass in a another good temperature successively (return value should be False)
+        ret = psu_status.set_temperature(31.456, 50.0)
+        assert ret == False
+        assert psu_status.temperature_good == True
+
+        # Pass in a high temperature
+        ret = psu_status.set_temperature(50.001, 50.0)
+        assert ret == True
+        assert psu_status.temperature_good == False
+
+        # Pass in a another bad temperature successively (return value should be False)
+        ret = psu_status.set_temperature(50.0, 50.0)
+        assert ret == False
+        assert psu_status.temperature_good == False
+
+        # Pass in a good (high edge case) temperature
+        ret = psu_status.set_temperature(49.999, 50.0)
+        assert ret == True
+        assert psu_status.temperature_good == True
+
+        # Test passing parameters as None when temperature_good == True
+        ret = psu_status.set_temperature(None, 50.0)
+        assert ret == False
+        assert psu_status.temperature_good == True
+        ret = psu_status.set_temperature(20.123, None)
+        assert ret == False
+        assert psu_status.temperature_good == True
+
+        # Test passing parameters as None when temperature_good == False
+        psu_status.temperature_good = False
+        ret = psu_status.set_temperature(None, 50.0)
+        assert ret == False
+        assert psu_status.temperature_good == True
+        psu_status.temperature_good = False
+        ret = psu_status.set_temperature(20.123, None)
+        assert ret == False
+        assert psu_status.temperature_good == True
+
+    def test_is_ok(self):
+        mock_logger = MagicMock()
+        mock_psu = MockPsu(True, True, "PSU 1")
+
+        psu_status = PsuStatus(mock_logger, mock_psu)
+        psu_status.presence = True
+        psu_status.power_good = True
+        psu_status.voltage_good = True
+        psu_status.temperature_good = True
+        ret = psu_status.is_ok()
+        assert ret == True
+
+        psu_status.presence = False
+        ret = psu_status.is_ok()
+        assert ret == False
+
+        psu_status.presence = True
+        ret = psu_status.is_ok()
+        assert ret == True
+
+        psu_status.power_good = False
+        ret = psu_status.is_ok()
+        assert ret == False
+
+        psu_status.power_good = True
+        ret = psu_status.is_ok()
+        assert ret == True
+
+        psu_status.voltage_good = False
+        ret = psu_status.is_ok()
+        assert ret == False
+
+        psu_status.voltage_good = True
+        ret = psu_status.is_ok()
+        assert ret == True
+
+        psu_status.temperature_good = False
+        ret = psu_status.is_ok()
+        assert ret == False
+
+        psu_status.temperature_good = True
+        ret = psu_status.is_ok()
+        assert ret == True

sonic-psud/tests/test_psud.py

@@ -2,7 +2,11 @@
 import sys
 from imp import load_source
 
-from mock import Mock, MagicMock, patch
+# TODO: Clean this up once we no longer need to support Python 2
+if sys.version_info.major == 3:
+    from unittest.mock import Mock, MagicMock, patch
+else:
+    from mock import Mock, MagicMock, patch
 from sonic_py_common import daemon_base
 
 from .mock_platform import MockChassis, MockPsu, MockFanDrawer, MockModule
@@ -169,3 +173,87 @@ def test_psuchassis_check_power_budget():
     assert float(fvs[CHASSIS_INFO_TOTAL_POWER_SUPPLIED_FIELD]) > float(fvs[CHASSIS_INFO_TOTAL_POWER_CONSUMED_FIELD])
     assert chassis_info.master_status_good == True
     assert MockPsu.get_status_master_led() == MockPsu.STATUS_LED_COLOR_GREEN
+
+
+def test_get_psu_key():
+    assert get_psu_key(0) == PSU_INFO_KEY_TEMPLATE.format(0)
+    assert get_psu_key(1) == PSU_INFO_KEY_TEMPLATE.format(1)
+
+
+def test_try_get():
+    # Test a proper, working callback
+    GOOD_CALLBACK_RETURN_VALUE = "This is a test"
+
+    def callback1():
+        return GOOD_CALLBACK_RETURN_VALUE
+
+    ret = try_get(callback1)
+    assert ret == GOOD_CALLBACK_RETURN_VALUE
+
+    # Ensure try_get returns default value if callback returns None
+    DEFAULT_VALUE = "Default value"
+
+    def callback2():
+        return None
+
+    ret = try_get(callback2, default=DEFAULT_VALUE)
+    assert ret == DEFAULT_VALUE
+
+    # Ensure try_get returns default value if callback returns None
+    def callback3():
+        raise NotImplementedError
+
+    ret = try_get(callback3, default=DEFAULT_VALUE)
+    assert ret == DEFAULT_VALUE
+
+
+class TestDaemonPsud(object):
+    """
+    Test cases to cover functionality in DaemonPsud class
+    """
+
+    def test_set_psu_led(self):
+        mock_logger = MagicMock()
+        mock_psu = MockPsu(True, True, "PSU 1")
+        psu_status = PsuStatus(mock_logger, mock_psu)
+
+        daemon_psud = DaemonPsud(SYSLOG_IDENTIFIER)
+
+        psu_status.presence = True
+        psu_status.power_good = True
+        psu_status.voltage_good = True
+        psu_status.temperature_good = True
+        daemon_psud._set_psu_led(mock_psu, psu_status)
+        assert mock_psu.get_status_led() == mock_psu.STATUS_LED_COLOR_GREEN
+
+        psu_status.presence = False
+        daemon_psud._set_psu_led(mock_psu, psu_status)
+        assert mock_psu.get_status_led() == mock_psu.STATUS_LED_COLOR_RED
+
+        psu_status.presence = True
+        daemon_psud._set_psu_led(mock_psu, psu_status)
+        assert mock_psu.get_status_led() == mock_psu.STATUS_LED_COLOR_GREEN
+
+        psu_status.power_good = False
+        daemon_psud._set_psu_led(mock_psu, psu_status)
+        assert mock_psu.get_status_led() == mock_psu.STATUS_LED_COLOR_RED
+
+        psu_status.power_good = True
+        daemon_psud._set_psu_led(mock_psu, psu_status)
+        assert mock_psu.get_status_led() == mock_psu.STATUS_LED_COLOR_GREEN
+
+        psu_status.voltage_good = False
+        daemon_psud._set_psu_led(mock_psu, psu_status)
+        assert mock_psu.get_status_led() == mock_psu.STATUS_LED_COLOR_RED
+
+        psu_status.voltage_good = True
+        daemon_psud._set_psu_led(mock_psu, psu_status)
+        assert mock_psu.get_status_led() == mock_psu.STATUS_LED_COLOR_GREEN
+
+        psu_status.temperature_good = False
+        daemon_psud._set_psu_led(mock_psu, psu_status)
+        assert mock_psu.get_status_led() == mock_psu.STATUS_LED_COLOR_RED
+
+        psu_status.temperature_good = True
+        daemon_psud._set_psu_led(mock_psu, psu_status)
+        assert mock_psu.get_status_led() == mock_psu.STATUS_LED_COLOR_GREEN