Apply patch [skip ci]

libs/core/tests/unit_tests/runnables/test_config.py

@@ -161,3 +161,91 @@ async def test_run_in_executor() -> None:
 
     with pytest.raises(RuntimeError):
         await run_in_executor(None, raises_stop_iter)
+
+
+def test_set_config_context_reuse_raises_error() -> None:
+    """Test that reusing the same context manager raises RuntimeError."""
+    from langchain_core.runnables.config import set_config_context
+    
+    config = RunnableConfig(tags=["test"])
+    ctx_manager = set_config_context(config)
+    
+    # First enter should work
+    with ctx_manager as ctx1:
+        assert ctx1 is not None
+        
+        # Second enter should raise RuntimeError
+        with pytest.raises(RuntimeError) as exc_info:
+            with ctx_manager as ctx2:
+                pass  # Should not reach here
+        
+        assert "Cannot re-enter an already-entered context manager" in str(exc_info.value)
+
+
+def test_set_config_context_exit_without_enter() -> None:
+    """Test that exiting without entering raises RuntimeError."""
+    from langchain_core.runnables.config import set_config_context
+    
+    config = RunnableConfig(tags=["test"])
+    ctx_manager = set_config_context(config)
+    
+    # Attempting to exit without entering should raise RuntimeError
+    with pytest.raises(RuntimeError) as exc_info:
+        ctx_manager.__exit__(None, None, None)
+    
+    assert "Cannot exit context manager that was not entered" in str(exc_info.value)
+
+
+def test_set_config_context_normal_usage() -> None:
+    """Test that normal usage still works correctly."""
+    from langchain_core.runnables.config import set_config_context
+    
+    config = RunnableConfig(
+        tags=["test"],
+        metadata={"key": "value"},
+        configurable={"param": "value"}
+    )
+    
+    # Normal usage should work without issues
+    with set_config_context(config) as ctx:
+        assert ctx is not None
+        # Context should be a contextvars.Context object
+        from contextvars import Context
+        assert isinstance(ctx, Context)
+    
+    # After exiting, we should be able to create a new context manager
+    # with the same config
+    with set_config_context(config) as ctx2:
+        assert ctx2 is not None
+        assert isinstance(ctx2, Context)
+
+
+def test_set_config_context_nested_different_instances() -> None:
+    """Test that using different instances in nested contexts works properly."""
+    from langchain_core.runnables.config import set_config_context
+    
+    config1 = RunnableConfig(
+        tags=["outer"],
+        metadata={"level": "outer"}
+    )
+    config2 = RunnableConfig(
+        tags=["inner"],
+        metadata={"level": "inner"}
+    )
+    
+    # Nested contexts with different instances should work
+    with set_config_context(config1) as ctx1:
+        assert ctx1 is not None
+        
+        with set_config_context(config2) as ctx2:
+            assert ctx2 is not None
+            # Both contexts should be valid
+            from contextvars import Context
+            assert isinstance(ctx1, Context)
+            assert isinstance(ctx2, Context)
+            # They should be different contexts
+            assert ctx1 is not ctx2
+        
+        # After inner context exits, outer should still be valid
+        assert ctx1 is not None
+