test: Add failing test for BaseCallbackManager.merge (#32040)

This pull request introduces a failing unit test to reproduce the bug
reported in issue #32028.
The test asserts the expected behavior: `BaseCallbackManager.merge()`
should combine `handlers` and `inheritable_handlers` independently,
without mixing them. This test will fail on the current codebase and is
intended to guide the fix and prevent future regressions.

---------

Co-authored-by: Eugene Yurtsev <eyurtsev@gmail.com>
Co-authored-by: Mason Daugherty <mason@langchain.dev>

libs/core/tests/unit_tests/callbacks/test_sync_callback_manager.py

@@ -1,3 +1,5 @@
+import pytest
+
 from langchain_core.callbacks.base import BaseCallbackHandler, BaseCallbackManager
 
 
@@ -13,3 +15,29 @@ def test_remove_handler() -> None:
     manager = BaseCallbackManager([handler1], inheritable_handlers=[handler2])
     manager.remove_handler(handler1)
     manager.remove_handler(handler2)
+
+
+@pytest.mark.xfail(
+    reason="TODO: #32028 merge() incorrectly mixes handlers and inheritable_handlers"
+)
+def test_merge_preserves_handler_distinction() -> None:
+    """Test that merging managers preserves the distinction between handlers.
+
+    This test verifies the correct behavior of the BaseCallbackManager.merge()
+    method. When two managers are merged, their handlers and
+    inheritable_handlers should be combined independently.
+
+    Currently, it is expected to xfail until the issue is resolved.
+    """
+    h1 = BaseCallbackHandler()
+    h2 = BaseCallbackHandler()
+    ih1 = BaseCallbackHandler()
+    ih2 = BaseCallbackHandler()
+
+    m1 = BaseCallbackManager(handlers=[h1], inheritable_handlers=[ih1])
+    m2 = BaseCallbackManager(handlers=[h2], inheritable_handlers=[ih2])
+
+    merged = m1.merge(m2)
+
+    assert set(merged.handlers) == {h1, h2}
+    assert set(merged.inheritable_handlers) == {ih1, ih2}

uv.lock

@@ -1,5 +1,5 @@
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-revision = 2
+revision = 3
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@@ -922,7 +922,6 @@ dependencies = [
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@@ -2478,7 +2477,7 @@ wheels = [
 
 [[package]]
 name = "langchain-core"
-version = "0.3.75"
+version = "0.3.76"
 source = { editable = "libs/core" }
 dependencies = [
     { name = "jsonpatch" },
@@ -2613,7 +2612,7 @@ dependencies = [
 
 [[package]]
 name = "langchain-groq"
-version = "0.3.7"
+version = "0.3.8"
 source = { editable = "libs/partners/groq" }
 dependencies = [
     { name = "groq" },
@@ -2814,7 +2813,7 @@ typing = []
 
 [[package]]
 name = "langchain-openai"
-version = "0.3.32"
+version = "0.3.33"
 source = { editable = "libs/partners/openai" }
 dependencies = [
     { name = "langchain-core" },
@@ -2825,7 +2824,7 @@ dependencies = [
 [package.metadata]
 requires-dist = [
     { name = "langchain-core", editable = "libs/core" },
-    { name = "openai", specifier = ">=1.99.9,<2.0.0" },
+    { name = "openai", specifier = ">=1.104.2,<2.0.0" },
     { name = "tiktoken", specifier = ">=0.7,<1" },
 ]
 
@@ -2880,18 +2879,14 @@ wheels = [
 
 [[package]]
 name = "langchain-text-splitters"
-version = "0.3.10"
+version = "0.3.11"
 source = { editable = "libs/text-splitters" }
 dependencies = [
     { name = "langchain-core" },
-    { name = "pip" },
 ]
 
 [package.metadata]
-requires-dist = [
+requires-dist = [{ name = "langchain-core", editable = "libs/core" }]
-    { name = "langchain-core", editable = "libs/core" },
-    { name = "pip", specifier = ">=25.2" },
-]
 
 [package.metadata.requires-dev]
 dev = [
@@ -2913,6 +2908,7 @@ test = [
     { name = "pytest-xdist", specifier = ">=3.6.1,<4.0.0" },
 ]
 test-integration = [
+    { name = "en-core-web-sm", url = "https://github.com/explosion/spacy-models/releases/download/en_core_web_sm-3.8.0/en_core_web_sm-3.8.0-py3-none-any.whl" },
     { name = "nltk", specifier = ">=3.9.1,<4.0.0" },
     { name = "sentence-transformers", specifier = ">=3.0.1" },
     { name = "spacy", specifier = ">=3.8.7,<4.0.0" },
@@ -2921,9 +2917,10 @@ test-integration = [
     { name = "transformers", specifier = ">=4.51.3,<5.0.0" },
 ]
 typing = [
+    { name = "beautifulsoup4", specifier = ">=4.13.5,<5.0.0" },
     { name = "lxml-stubs", specifier = ">=0.5.1,<1.0.0" },
     { name = "mypy", specifier = ">=1.17.1,<1.18" },
-    { name = "tiktoken", specifier = ">=0.8.0,<1.0.0" },
+    { name = "tiktoken", specifier = ">=0.11.0,<1.0.0" },
     { name = "types-requests", specifier = ">=2.31.0.20240218,<3.0.0.0" },
 ]
 
@@ -3971,7 +3968,7 @@ wheels = [
 
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+version = "1.107.1"
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@@ -3983,9 +3980,9 @@ dependencies = [
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