fix: Swap unit test sleeps with explicit signaling

tests/strands/agent/test_agent.py

@@ -1,14 +1,13 @@
-import asyncio
 import copy
 import importlib
 import json
 import os
 import textwrap
 import threading
-import time
 import unittest.mock
 import warnings
-from typing import Any, AsyncGenerator
+from collections.abc import AsyncGenerator
+from typing import Any
 from uuid import uuid4
 
 import pytest
@@ -193,11 +192,25 @@ class User(BaseModel):
     return User(name="Jane Doe", age=30, email="jane@doe.com")
 
 
-class SlowMockedModel(MockedModelProvider):
+class SyncEventMockedModel(MockedModelProvider):
+    """A mock model that uses events to synchronize concurrent threads.
+
+    This model signals when it starts streaming and waits for a proceed signal,
+    allowing deterministic testing of concurrent behavior without relying on sleeps.
+    """
+
+    def __init__(self, agent_responses):
+        super().__init__(agent_responses)
+        self.started_event = threading.Event()
+        self.proceed_event = threading.Event()
+
     async def stream(
         self, messages, tool_specs=None, system_prompt=None, tool_choice=None, **kwargs
     ) -> AsyncGenerator[Any, None]:
-        await asyncio.sleep(0.15)  # Add async delay to ensure concurrency
+        # Signal that streaming has started
+        self.started_event.set()
+        # Wait for signal to proceed
+        self.proceed_event.wait()
         async for event in super().stream(messages, tool_specs, system_prompt, tool_choice, **kwargs):
             yield event
 
@@ -2212,7 +2225,7 @@ def test_agent_skips_fix_for_valid_conversation(mock_model, agenerator):
 
 def test_agent_concurrent_call_raises_exception():
     """Test that concurrent __call__() calls raise ConcurrencyException."""
-    model = SlowMockedModel(
+    model = SyncEventMockedModel(
         [
             {"role": "assistant", "content": [{"text": "hello"}]},
             {"role": "assistant", "content": [{"text": "world"}]},
@@ -2233,12 +2246,20 @@ def invoke():
             with lock:
                 errors.append(e)
 
-    # Create two threads that will try to invoke concurrently
+    # Start first thread and wait for it to begin streaming
     t1 = threading.Thread(target=invoke)
-    t2 = threading.Thread(target=invoke)
-
     t1.start()
+    model.started_event.wait()  # Wait until first thread is in the model.stream()
+
+    # Start second thread while first is still running
+    t2 = threading.Thread(target=invoke)
     t2.start()
+
+    # Give second thread time to attempt invocation and fail
+    t2.join(timeout=1.0)
+
+    # Now let first thread complete
+    model.proceed_event.set()
     t1.join()
     t2.join()
 
@@ -2254,11 +2275,12 @@ def test_agent_concurrent_structured_output_raises_exception():
     Note: This test validates that the sync invocation path is protected.
     The concurrent __call__() test already validates the core functionality.
     """
-    model = SlowMockedModel(
+    # Events for synchronization
+    model = SyncEventMockedModel(
         [
             {"role": "assistant", "content": [{"text": "response1"}]},
             {"role": "assistant", "content": [{"text": "response2"}]},
-        ]
+        ],
     )
     agent = Agent(model=model)
 
@@ -2275,13 +2297,20 @@ def invoke():
             with lock:
                 errors.append(e)
 
-    # Create two threads that will try to invoke concurrently
+    # Start first thread and wait for it to begin streaming
     t1 = threading.Thread(target=invoke)
-    t2 = threading.Thread(target=invoke)
-
     t1.start()
-    time.sleep(0.05)  # Small delay to ensure first thread acquires lock
+    model.started_event.wait()  # Wait until first thread is in the model.stream()
+
+    # Start second thread while first is still running
+    t2 = threading.Thread(target=invoke)
     t2.start()
+
+    # Give second thread time to attempt invocation and fail
+    t2.join(timeout=1.0)
+
+    # Now let first thread complete
+    model.proceed_event.set()
     t1.join()
     t2.join()