Add test for `LinkedTaskChannel.subscribe()` fanout feature

tests/test_infected_asyncio.py

@@ -2,9 +2,10 @@
 The hipster way to force SC onto the stdlib's "async": 'infection mode'.
 
 '''
-from typing import Optional, Iterable
+from typing import Optional, Iterable, Union
 import asyncio
 import builtins
+import itertools
 import importlib
 
 import pytest
@@ -12,6 +13,7 @@ import trio
 import tractor
 from tractor import to_asyncio
 from tractor import RemoteActorError
+from tractor.trionics import BroadcastReceiver
 
 
 async def sleep_and_err(sleep_for: float = 0.1):
@@ -217,6 +219,7 @@ async def stream_from_aio(
     exit_early: bool = False,
     raise_err: bool = False,
     aio_raise_err: bool = False,
+    fan_out: bool = False,
 
 ) -> None:
     seq = range(100)
@@ -234,6 +237,12 @@ async def stream_from_aio(
 
             assert first is True
 
+            async def consume(
+                chan: Union[
+                    to_asyncio.LinkedTaskChannel,
+                    BroadcastReceiver,
+                ],
+            ):
                 async for value in chan:
                     print(f'trio received {value}')
                     pulled.append(value)
@@ -243,6 +252,18 @@ async def stream_from_aio(
                             raise Exception
                         elif exit_early:
                             break
+
+            if fan_out:
+                # start second task that get's the same stream value set.
+                async with (
+                    trio.open_nursery() as n,
+                    chan.subscribe() as br,
+                ):
+                    n.start_soon(consume, br)
+                    await consume(chan)
+
+            else:
+                await consume(chan)
     finally:
 
         if (
@@ -250,19 +271,32 @@ async def stream_from_aio(
             not exit_early and
             not aio_raise_err
         ):
+            if fan_out:
+                # we get double the pulled values in the
+                # ``.subscribe()`` fan out case.
+                doubled = list(itertools.chain(*zip(expect, expect)))
+                assert pulled == doubled
+
+            else:
                 assert pulled == expect
         else:
+            # if fan_out:
             assert pulled == expect[:51]
 
         print('trio guest mode task completed!')
 
 
-def test_basic_interloop_channel_stream(arb_addr):
+@pytest.mark.parametrize(
+    'fan_out', [False, True],
+    ids='fan_out_w_chan_subscribe={}'.format
+)
+def test_basic_interloop_channel_stream(arb_addr, fan_out):
     async def main():
         async with tractor.open_nursery() as n:
             portal = await n.run_in_actor(
                 stream_from_aio,
                 infect_asyncio=True,
+                fan_out=fan_out,
             )
             await portal.result()