Added tests for select & select many

src/cpl_query/extension/iterable_abc.py

@@ -158,7 +158,7 @@ class IterableABC(ABC, list):
         """
         pass
 
-    def extend(self, __iterable: Iterable) -> None:
+    def extend(self, __iterable: Iterable) -> 'IterableABC':
         r"""Adds elements of given list to list
 
         Parameter
@@ -169,6 +169,8 @@ class IterableABC(ABC, list):
         for value in __iterable:
             self.append(value)
 
+        return self
+
     @abstractmethod
     def last(self) -> any:
         r"""Returns last element
@@ -290,6 +292,24 @@ class IterableABC(ABC, list):
         """
         pass
 
+    def select(self, _f: Callable) -> 'IterableABC':
+        r"""Formats each element of list to a given format
+
+        Returns
+        -------
+            :class: `cpl_query.extension.iterable_abc.IterableABC`
+        """
+        pass
+
+    def select_many(self, _f: Callable) -> 'IterableABC':
+        r"""Flattens resulting lists to one
+
+        Returns
+        -------
+            :class: `cpl_query.extension.iterable_abc.IterableABC`
+        """
+        pass
+
     @abstractmethod
     def single(self) -> any:
         r"""Returns one single element of list