Add stale entry deleted from registrar test

By spawning an actor task that immediately shuts down the transport
server and then sleeps, verify that attempting to connect via the
`._discovery.find_actor()` helper delivers `None` for the `Portal`
value.

Relates to #184 and #216

tests/test_discovery.py

@@ -1,7 +1,7 @@
-"""
-Discovery subsys.
+'''
+Discovery subsystem via a "registrar" actor scenarios.
 
-"""
+'''
 import os
 import signal
 import platform
@@ -163,7 +163,10 @@ async def unpack_reg(
     else:
         msg = await actor_or_portal.run_from_ns('self', 'get_registry')
 
-    return {tuple(key.split('.')): val for key, val in msg.items()}
+    return {
+        tuple(key.split('.')): val
+        for key, val in msg.items()
+    }
 
 
 async def spawn_and_check_registry(
@@ -356,20 +359,24 @@ async def close_chans_before_nursery(
             try:
                 get_reg = partial(unpack_reg, aportal)
 
-                async with tractor.open_nursery() as tn:
-                    portal1 = await tn.start_actor(
-                        name='consumer1', enable_modules=[__name__])
-                    portal2 = await tn.start_actor(
-                        'consumer2', enable_modules=[__name__])
+                async with tractor.open_nursery() as an:
+                    portal1 = await an.start_actor(
+                        name='consumer1',
+                        enable_modules=[__name__],
+                    )
+                    portal2 = await an.start_actor(
+                        'consumer2',
+                        enable_modules=[__name__],
+                    )
 
-                    # TODO: compact this back as was in last commit once
-                    # 3.9+, see https://github.com/goodboy/tractor/issues/207
-                    async with portal1.open_stream_from(
+                    async with (
+                        portal1.open_stream_from(
                             stream_forever
-                    ) as agen1:
-                        async with portal2.open_stream_from(
+                        ) as agen1,
+                        portal2.open_stream_from(
                             stream_forever
-                        ) as agen2:
+                        ) as agen2,
+                    ):
                             async with (
                                 collapse_eg(),
                                 trio.open_nursery() as tn,
@@ -392,6 +399,7 @@ async def close_chans_before_nursery(
                                     # also kill off channels cuz why not
                                     await agen1.aclose()
                                     await agen2.aclose()
+
             finally:
                 with trio.CancelScope(shield=True):
                     await trio.sleep(1)
@@ -427,7 +435,7 @@ def test_close_channel_explicit(
 
 
 @pytest.mark.parametrize('use_signal', [False, True])
-def test_close_channel_explicit_remote_arbiter(
+def test_close_channel_explicit_remote_registrar(
     daemon: subprocess.Popen,
     start_method: str,
     use_signal: bool,
@@ -448,3 +456,61 @@ def test_close_channel_explicit_remote_arbiter(
                 remote_arbiter=True,
             ),
         )
+
+
+@tractor.context
+async def kill_transport(
+    ctx: tractor.Context,
+) -> None:
+
+    await ctx.started()
+    actor: tractor.Actor = tractor.current_actor()
+    actor.ipc_server.cancel()
+    await trio.sleep_forever()
+
+
+
+# @pytest.mark.parametrize('use_signal', [False, True])
+def test_stale_entry_is_deleted(
+    debug_mode: bool,
+    daemon: subprocess.Popen,
+    start_method: str,
+    reg_addr: tuple,
+):
+    '''
+    Ensure that when a stale entry is detected in the registrar's
+    table that the `find_actor()` API takes care of deleting the
+    stale entry and not delivering a bad portal.
+
+    '''
+    async def main():
+
+        name: str = 'transport_fails_actor'
+        _reg_ptl: tractor.Portal
+        an: tractor.ActorNursery
+        async with (
+            tractor.open_nursery(
+                debug_mode=debug_mode,
+            ) as an,
+            tractor.get_registry(reg_addr) as _reg_ptl,
+        ):
+            ptl: tractor.Portal = await an.start_actor(
+                name,
+                enable_modules=[__name__],
+            )
+            async with ptl.open_context(
+                kill_transport,
+            ) as (first, ctx):
+                async with tractor.find_actor(name) as maybe_portal:
+                    # because the transitive
+                    # `._discovery.maybe_open_portal()` call should
+                    # fail and implicitly call `.delete_sockaddr()`
+                    assert maybe_portal is None
+                    registry: dict = await unpack_reg(_reg_ptl)
+                    assert ptl.chan.aid.uid not in registry
+
+                # should fail since we knocked out the IPC tpt XD
+                await ptl.cancel_actor()
+                await an.cancel()
+
+    trio.run(main)