Split execution module in submodules for better readability.

bonobo/util/iterators.py

@@ -20,4 +20,10 @@ def force_iterator(mixed):
 def ensure_tuple(tuple_or_mixed):
     if isinstance(tuple_or_mixed, tuple):
         return tuple_or_mixed
-    return (tuple_or_mixed,)
+    return (tuple_or_mixed,)
+
+
+def iter_if_not_sequence(mixed):
+    if isinstance(mixed, (dict, list, str)):
+        raise TypeError(type(mixed).__name__)
+    return iter(mixed)

bonobo/util/testing.py

@@ -1,6 +1,6 @@
 from unittest.mock import MagicMock
 
-from bonobo.execution import NodeExecutionContext
+from bonobo.execution.node import NodeExecutionContext
 
 
 class CapturingNodeExecutionContext(NodeExecutionContext):