Fix lock property and add test coverage for RunUsage + RequestUsage

- Fix _lock property to check for '_RunUsage__lock' instead of '__lock'
  (hasattr with '__lock' string doesn't get name-mangled, so it always returned False)
- Add test_run_usage_with_request_usage() to cover:
  * RunUsage.__add__(RequestUsage) - line 232->236 branch
  * RunUsage.incr(RequestUsage) - line 212->216 branch
  * Multiple accesses to _lock property - line 198->200 branch
- Achieves 100% test coverage for usage.py

Author: certainly-param

pydantic_ai_slim/pydantic_ai/usage.py

@@ -195,7 +195,7 @@ class RunUsage(UsageBase):
     @property
     def _lock(self) -> threading.Lock:
         """Get the lock, creating it if it doesn't exist."""
-        if not hasattr(self, '__lock'):
+        if not hasattr(self, '_RunUsage__lock'):
             self.__lock = threading.Lock()
         return self.__lock
 

tests/test_usage_limits.py

@@ -248,6 +248,34 @@ def test_add_usages():
     assert RunUsage() + RunUsage() == RunUsage()
 
 
+def test_run_usage_with_request_usage():
+    """Test RunUsage operations with RequestUsage to ensure coverage of RequestUsage branches."""
+    run_usage = RunUsage(requests=1, input_tokens=10, output_tokens=20, tool_calls=1)
+    request_usage = RequestUsage(input_tokens=5, output_tokens=10)
+    
+    # Test __add__ with RequestUsage (covers line 232->236 branch)
+    result = run_usage + request_usage
+    assert result.requests == 2  # 1 + 1 (RequestUsage.requests property returns 1)
+    assert result.input_tokens == 15
+    assert result.output_tokens == 30
+    assert result.tool_calls == 1  # RequestUsage doesn't have tool_calls
+    
+    # Test incr with RequestUsage (covers line 212->216 branch)
+    run_usage2 = RunUsage(requests=2, input_tokens=20, output_tokens=30, tool_calls=2)
+    run_usage2.incr(request_usage)
+    assert run_usage2.requests == 3  # 2 + 1
+    assert run_usage2.input_tokens == 25  # 20 + 5
+    assert run_usage2.output_tokens == 40  # 30 + 10
+    assert run_usage2.tool_calls == 2  # Unchanged
+    
+    # Test accessing _lock multiple times on same instance (covers line 198->200 branch)
+    # First access creates the lock
+    lock1 = run_usage._lock
+    # Second access returns the existing lock (covers the hasattr return path)
+    lock2 = run_usage._lock
+    assert lock1 is lock2  # Same lock instance
+
+
 async def test_tool_call_limit() -> None:
     test_agent = Agent(TestModel())