feat, wip: refactoring and simplification of how casts are made.

tests/nodes/test_casts.py

@@ -0,0 +1,65 @@
+from collections import namedtuple
+from typing import Callable
+
+import pytest
+
+from bonobo.constants import EMPTY
+from bonobo.util.bags import BagType
+from bonobo.util.envelopes import Envelope
+from bonobo.util.testing import BufferingNodeExecutionContext
+
+MyTuple = namedtuple('MyTuple', ['a', 'b', 'c'])
+MyBag = BagType('MyBag', ['a', 'b', 'c'])
+
+
+class MyCustomType():
+    def __init__(self, *args):
+        self.args = args
+
+    def as_tuple(self):
+        return MyBag(*self.args)
+
+
+@pytest.mark.parametrize(['factory', 'expected', 'expected_item0'], [
+    [lambda: (1, 2, 3), tuple, int],
+    [lambda: Envelope((1, 2, 3)), tuple, int],
+    [lambda: MyTuple(1, 2, 3), MyTuple, int],
+    [lambda: Envelope(MyTuple(1, 2, 3)), MyTuple, int],
+    [lambda: MyBag(1, 2, 3), MyBag, int],
+    [lambda: Envelope(MyBag(1, 2, 3)), MyBag, int],
+    [lambda: MyCustomType(1, 2, 3), tuple, MyCustomType],
+    [lambda: Envelope(MyCustomType(1, 2, 3)), tuple, MyCustomType],
+])
+def test_casts_after_output(factory: Callable, expected, expected_item0):
+    def transform():
+        yield factory()
+        yield factory()
+
+    with BufferingNodeExecutionContext(transform) as context:
+        context.write_sync(EMPTY)
+
+    result = context.get_buffer()
+    assert expected == type(result[0])
+    assert expected_item0 == type(result[0][0])
+    assert expected == type(result[1])
+    assert expected_item0 == type(result[1][0])
+
+
+def test_cast_after_returning_custom_type():
+    def transform():
+        yield MyCustomType(1, 2, 3)
+        yield MyCustomType(4, 5, 6)
+
+    with BufferingNodeExecutionContext(transform) as context:
+        context.write_sync(EMPTY)
+    result = context.get_buffer()
+    assert tuple == type(result[0])
+    assert tuple == type(result[1])
+    assert MyCustomType == type(result[0][0])
+    assert MyCustomType == type(result[1][0])
+
+    with BufferingNodeExecutionContext(MyCustomType.as_tuple) as context:
+        context.write_sync(*result)
+    result = context.get_buffer()
+    assert MyBag == type(result[0])
+    assert MyBag == type(result[1])