core[minor]: add langsmith document loader (#25493)

needs tests

libs/core/tests/unit_tests/document_loaders/test_langsmith.py

@@ -0,0 +1,58 @@
+import datetime
+import uuid
+from unittest.mock import MagicMock, patch
+
+from langsmith.schemas import Example
+
+from langchain_core.document_loaders import LangSmithLoader
+from langchain_core.documents import Document
+
+
+def test_init() -> None:
+    LangSmithLoader(api_key="secret")
+
+
+EXAMPLES = [
+    Example(
+        inputs={"first": {"second": "foo"}},
+        outputs={"res": "a"},
+        dataset_id=uuid.uuid4(),
+        id=uuid.uuid4(),
+        created_at=datetime.datetime.now(),
+    ),
+    Example(
+        inputs={"first": {"second": "bar"}},
+        outputs={"res": "b"},
+        dataset_id=uuid.uuid4(),
+        id=uuid.uuid4(),
+        created_at=datetime.datetime.now(),
+    ),
+    Example(
+        inputs={"first": {"second": "baz"}},
+        outputs={"res": "c"},
+        dataset_id=uuid.uuid4(),
+        id=uuid.uuid4(),
+        created_at=datetime.datetime.now(),
+    ),
+]
+
+
+@patch("langsmith.Client.list_examples", MagicMock(return_value=iter(EXAMPLES)))
+def test_lazy_load() -> None:
+    loader = LangSmithLoader(
+        api_key="dummy",
+        dataset_id="mock",
+        content_key="first.second",
+        format_content=(lambda x: x.upper()),
+    )
+    expected = []
+    for example in EXAMPLES:
+        metadata = {
+            k: v if not v or isinstance(v, dict) else str(v)
+            for k, v in example.dict().items()
+        }
+        expected.append(
+            Document(example.inputs["first"]["second"].upper(), metadata=metadata)
+        )
+    actual = [doc for doc in loader.lazy_load()]
+    assert expected == actual