standard-tests[minor]: Add standard tests for BaseStore (#23360)

Add standard tests to base store abstraction. These only work on [str,
str] right now. We'll need to check if it's possible to add
encoder/decoders to generalize

libs/standard-tests/tests/unit_tests/test_in_memory_base_store.py

@@ -0,0 +1,30 @@
+"""Tests for the InMemoryStore class."""
+from typing import Tuple
+
+import pytest
+from langchain_core.stores import InMemoryStore
+
+from langchain_standard_tests.integration_tests.base_store import (
+    BaseStoreAsyncTests,
+    BaseStoreSyncTests,
+)
+
+
+class TestInMemoryStore(BaseStoreSyncTests):
+    @pytest.fixture
+    def three_values(self) -> Tuple[str, str, str]:
+        return "foo", "bar", "buzz"
+
+    @pytest.fixture
+    def kv_store(self) -> InMemoryStore:
+        return InMemoryStore()
+
+
+class TestInMemoryStoreAsync(BaseStoreAsyncTests):
+    @pytest.fixture
+    def three_values(self) -> Tuple[str, str, str]:  # type: ignore
+        return "foo", "bar", "buzz"
+
+    @pytest.fixture
+    async def kv_store(self) -> InMemoryStore:
+        return InMemoryStore()