test __post_init__ (#114)

* test `__post_init__`

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* replace with typing

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---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

tests/test_post_init.py

@@ -0,0 +1,29 @@
+import dataclasses
+import znflow
+import typing as t
+
+
+@dataclasses.dataclass
+class NodeWithPostInit(znflow.Node):
+    input: int
+    output: t.Optional[int] = None
+
+    def __post_init__(self):
+        self.input = self.input * 2
+
+    def run(self):
+        self.output = self.input + 1
+
+
+def test_post_init():
+    graph = znflow.DiGraph()
+
+    with graph:
+        node = NodeWithPostInit(input=10)
+
+    assert node.input == 20
+
+    graph.run()
+
+    assert node.output == 21
+    assert node.input == 20