@Override
    public Object getInternalProperty(String key) {
        return System.getProperty(key);
    }
@Test
    void testGetSysProperty() {
        Assertions.assertNull(sysConfig.getInternalProperty(MOCK_KEY));
        Assertions.assertFalse(sysConfig.containsKey(MOCK_KEY));
        Assertions.assertNull(sysConfig.getString(MOCK_KEY));
        Assertions.assertNull(sysConfig.getProperty(MOCK_KEY));
        System.setProperty(MOCK_KEY, MOCK_STRING_VALUE);
        Assertions.assertTrue(sysConfig.containsKey(MOCK_KEY));
        Assertions.assertEquals(MOCK_STRING_VALUE, sysConfig.getInternalProperty(MOCK_KEY));
        Assertions.assertEquals(MOCK_STRING_VALUE, sysConfig.getString(MOCK_KEY, MOCK_STRING_VALUE));
        Assertions.assertEquals(MOCK_STRING_VALUE, sysConfig.getProperty(MOCK_KEY, MOCK_STRING_VALUE));
    }