diff --git a/tests/test_context_streams.py b/tests/test_context_streams.py
index e1d4de4..48ccbc8 100644
--- a/tests/test_context_streams.py
+++ b/tests/test_context_streams.py
@@ -5,9 +5,10 @@ Verify the we raise errors when streams are opened prior to sync-opening
 a ``tractor.Context`` beforehand.
 
 '''
+from itertools import count
+
 import pytest
 import trio
-from trio.lowlevel import current_task
 import tractor
 
 
@@ -18,7 +19,7 @@ async def really_started(
     await ctx.started()
     try:
         await ctx.started()
-    except RuntimeError as err:
+    except RuntimeError:
         raise
 
 
@@ -32,9 +33,10 @@ def test_started_called_more_then_once():
             )
 
             async with portal.open_context(really_started) as (ctx, sent):
-                pass
+                await trio.sleep(1)
+                # pass
 
-    with pytest.raises(tractor.RemoteActorError) as excinfo:
+    with pytest.raises(tractor.RemoteActorError):
         trio.run(main)
 
 
@@ -44,20 +46,50 @@ async def never_open_stream(
     ctx:  tractor.Context,
 
 ) -> None:
-    '''Bidir streaming endpoint which will stream
-    back any sequence it is sent item-wise.
+    '''
+    Context which never opens a stream and blocks.
 
     '''
     await ctx.started()
     await trio.sleep_forever()
 
 
-def test_no_far_end_stream_opened():
+@tractor.context
+async def keep_sending_from_callee(
+
+    ctx:  tractor.Context,
+
+) -> None:
+    '''
+    Send endlessly on the calleee stream.
+
+    '''
+    await ctx.started()
+    async with ctx.open_stream() as stream:
+        for msg in count():
+            await stream.send(msg)
+            await trio.sleep(0.01)
+
+
+@pytest.mark.parametrize(
+    'overrun_by',
+    [
+        (None, 0, never_open_stream),  # use default settings
+        ('caller', 1, never_open_stream),
+        ('callee', 0, keep_sending_from_callee),
+    ],
+    ids='overrun_condition_by={}'.format,
+)
+def test_one_end_stream_not_opened(overrun_by):
     '''
     This should exemplify the bug from:
     https://github.com/goodboy/tractor/issues/265
 
     '''
+    overrunner, buf_size_increase, entrypoint = overrun_by
+    from tractor._actor import Actor
+    buf_size = buf_size_increase + Actor.msg_buffer_size
+
     async def main():
         async with tractor.open_nursery() as n:
             portal = await n.start_actor(
@@ -65,23 +97,37 @@ def test_no_far_end_stream_opened():
                 enable_modules=[__name__],
             )
 
-            async with (
-                portal.open_context(
-                    never_open_stream,) as (ctx, sent),
-                ctx.open_stream() as stream,
-            ):
+            async with portal.open_context(entrypoint) as (ctx, sent):
                 assert sent is None
 
-                # XXX: so the question is whether
-                # this should error if the far end
-                # has not yet called `ctx.open_stream()`?
-                # If we decide to do that we need a synchronization
-                # message which is sent from that call?
-                await stream.send('yo')
+                if overrunner in (None, 'caller'):
+
+                    async with ctx.open_stream() as stream:
+                        for i in range(buf_size - 1):
+                            await stream.send('yo')
+
+                else:
+                    # callee overruns caller case so we do nothing here
+                    await trio.sleep_forever()
 
                 # without this we block waiting on the child side
                 await ctx.cancel()
 
             await portal.cancel_actor()
 
-    trio.run(main)
+    # 2 overrun cases and the no overrun case (which pushes right up to
+    # the msg limit)
+    if overrunner == 'caller':
+        with pytest.raises(tractor.RemoteActorError) as excinfo:
+            trio.run(main)
+
+        assert excinfo.value.type == tractor._exceptions.StreamOverrun
+
+    elif overrunner == 'callee':
+        with pytest.raises(tractor.RemoteActorError) as excinfo:
+            trio.run(main)
+
+        assert excinfo.value.type == tractor.RemoteActorError
+
+    else:
+        trio.run(main)