implement getInstance class method to pass test_get_instance fix #5

config_provider.py

 class ConfigProvider:
 
+  _instance = None
+
+  @classmethod
+  def getInstance(cls):
+    return ConfigProvider._instance
+
   def __init__(self, load_function):
     self._conf_dict = load_function['function'](
       *load_function.get('args'), **load_function.get('kwargs'))
     self._load_function = load_function
+    ConfigProvider._instance = self
 
   @property
   def dict(self):