Added tests and docstrings to fibonacci_heap.py

Author: mcawezome

data_structures/heap/fibonacci_heap.py

@@ -294,7 +294,7 @@ def decrease_key(self, node, new_val):
 
     def __cut(self, node, parent):
         """
-        Cuts a node from its parent.
+        Cuts a node from its parent
 
         Args:
             node: Node to be cut.