fix: correct MultiTurnSample user_input validation logic

   Fixed validation bug where generator expression was not being evaluated.
   Changed from checking generator object to using all() to properly validate
   all messages are instances of HumanMessage, AIMessage, or ToolMessage.

   Added tests to verify validation works correctly.

Author: harshil-sanghvi

src/ragas/dataset_schema.py

@@ -128,7 +128,7 @@ def validate_user_input(
         messages: t.List[t.Union[HumanMessage, AIMessage, ToolMessage]],
     ) -> t.List[t.Union[HumanMessage, AIMessage, ToolMessage]]:
         """Validates the user input messages."""
-        if not (
+        if not all(
             isinstance(m, (HumanMessage, AIMessage, ToolMessage)) for m in messages
         ):
             raise ValueError(

tests/unit/test_dataset_schema.py

@@ -196,3 +196,31 @@ def test_evaluation_dataset_type():
 
     dataset = EvaluationDataset(samples=[multi_turn_sample])
     assert dataset.get_sample_type() == MultiTurnSample
+
+
+def test_multiturn_sample_validate_user_input_invalid_type():
+    """Test that MultiTurnSample validation correctly rejects invalid message types."""
+    from pydantic import ValidationError
+
+    with pytest.raises(ValidationError):
+        MultiTurnSample(
+            user_input=[
+                HumanMessage(content="Hello"),
+                "invalid_string",  # This should be rejected by Pydantic
+            ]
+        )
+
+
+def test_multiturn_sample_validate_user_input_valid_types():
+    """Test that MultiTurnSample validation accepts valid message types."""
+    from ragas.messages import AIMessage
+
+    sample = MultiTurnSample(
+        user_input=[
+            HumanMessage(content="Hello"),
+            AIMessage(content="Hi there"),
+        ]
+    )
+    assert len(sample.user_input) == 2
+    assert isinstance(sample.user_input[0], HumanMessage)
+    assert isinstance(sample.user_input[1], AIMessage)