mistralai: Add langchain-mistralai partner package (#14783)

Co-authored-by: Chad Phillips <chad@apartmentlines.com>

libs/partners/mistralai/tests/unit_tests/test_chat_models.py

@@ -0,0 +1,65 @@
+"""Test MistralAI Chat API wrapper."""
+import os
+
+import pytest
+from langchain_core.messages import (
+    AIMessage,
+    BaseMessage,
+    ChatMessage,
+    HumanMessage,
+    SystemMessage,
+)
+
+# TODO: Remove 'type: ignore' once mistralai has stubs or py.typed marker.
+from mistralai.models.chat_completion import (  # type: ignore[import]
+    ChatMessage as MistralChatMessage,
+)
+
+from langchain_mistralai.chat_models import (  # type: ignore[import]
+    ChatMistralAI,
+    _convert_message_to_mistral_chat_message,
+)
+
+os.environ["MISTRAL_API_KEY"] = "foo"
+
+
+@pytest.mark.requires("mistralai")
+def test_mistralai_model_param() -> None:
+    llm = ChatMistralAI(model="foo")
+    assert llm.model == "foo"
+
+
+@pytest.mark.requires("mistralai")
+def test_mistralai_initialization() -> None:
+    """Test ChatMistralAI initialization."""
+    # Verify that ChatMistralAI can be initialized using a secret key provided
+    # as a parameter rather than an environment variable.
+    ChatMistralAI(model="test", mistral_api_key="test")
+
+
+@pytest.mark.parametrize(
+    ("message", "expected"),
+    [
+        (
+            SystemMessage(content="Hello"),
+            MistralChatMessage(role="system", content="Hello"),
+        ),
+        (
+            HumanMessage(content="Hello"),
+            MistralChatMessage(role="user", content="Hello"),
+        ),
+        (
+            AIMessage(content="Hello"),
+            MistralChatMessage(role="assistant", content="Hello"),
+        ),
+        (
+            ChatMessage(role="assistant", content="Hello"),
+            MistralChatMessage(role="assistant", content="Hello"),
+        ),
+    ],
+)
+def test_convert_message_to_mistral_chat_message(
+    message: BaseMessage, expected: MistralChatMessage
+) -> None:
+    result = _convert_message_to_mistral_chat_message(message)
+    assert result == expected