test: add regression test for issue #509 example

Author: fgmacedo

tests/testcases/test_issue509.py

@@ -0,0 +1,65 @@
+"""
+
+### Issue 509
+
+A StateChart that exercises the example given on issue
+#[509](https://github.com/fgmacedo/python-statemachine/issues/509).
+
+When multiple async coroutines send events concurrently, each caller should
+receive its own event's result or exception — not another caller's.
+
+Original problem: fn2 triggers a validator exception, but fn1 receives it instead.
+"""
+
+import asyncio
+
+import pytest
+
+from statemachine import State
+from statemachine import StateChart
+
+
+class Issue509SC(StateChart):
+    error_on_execution = False
+
+    INITIAL = State(initial=True)
+    FINAL = State()
+
+    noop = INITIAL.to(FINAL, on="do_nothing")
+    noop2 = INITIAL.to(FINAL, on="do_nothing", validators="raise_exception") | FINAL.to.itself(
+        on="do_nothing", validators="raise_exception"
+    )
+
+    async def do_nothing(self, name):
+        await asyncio.sleep(0.1)
+        return f"Did nothing via {name}"
+
+    def raise_exception(self):
+        raise ValueError("noop2 is not allowed")
+
+
+@pytest.mark.asyncio()
+async def test_issue509_exception_routed_to_correct_caller():
+    test = Issue509SC()
+    await test.activate_initial_state()
+
+    results = {}
+
+    async def fn1():
+        results["fn1"] = await test.send("noop", "fn1")
+
+    async def fn2():
+        try:
+            await test.send("noop2", "fn2")
+            results["fn2"] = "no error"
+        except ValueError as e:
+            results["fn2"] = f"caught: {e}"
+
+    task1 = asyncio.create_task(fn1())
+    task2 = asyncio.create_task(fn2())
+    await asyncio.gather(task1, task2)
+
+    # fn1 should get its own result, not fn2's exception
+    assert results["fn1"] == "Did nothing via fn1"
+    # fn2 should catch the ValueError from its own validator
+    assert results["fn2"] == "caught: noop2 is not allowed"