test: add test for agent async fn to increase coverage (#16331)

-test: add unit test for async fn custom agent to increase coverage

llama-index-core/tests/agent/custom/test_simple_function.py

@@ -1,9 +1,13 @@
 """Test simple function agent."""
 
 from typing import Any, Dict, Tuple
-
-from llama_index.core.agent.custom.simple_function import FnAgentWorker
 import pytest
+from llama_index.core.agent.custom.simple_function import FnAgentWorker
+
+
+def mock_foo_fn_no_state_param() -> Tuple[None, bool]:
+    """Mock agent input function without a state."""
+    return None, True
 
 
 def mock_foo_fn(state: dict) -> Tuple[Dict[str, Any], bool]:
@@ -25,6 +29,11 @@ def mock_foo_fn(state: dict) -> Tuple[Dict[str, Any], bool]:
     return state, is_done
 
 
+async def async_mock_foo_fn(state: dict) -> Tuple[Dict[str, Any], bool]:
+    """Mock async agent input function."""
+    return mock_foo_fn(state)
+
+
 def test_fn_agent() -> None:
     """Test function agent."""
     agent = FnAgentWorker(fn=mock_foo_fn, initial_state={"max_count": 5}).as_agent()
@@ -34,3 +43,32 @@ def test_fn_agent() -> None:
     with pytest.raises(ValueError):
         agent = FnAgentWorker(fn=mock_foo_fn).as_agent()
         response = agent.query("hello")
+
+
+def test_fn_agent_init() -> None:
+    """Test function agent init."""
+    with pytest.raises(ValueError) as error_info:
+        FnAgentWorker(fn=mock_foo_fn_no_state_param).as_agent()
+
+    assert (
+        str(error_info.value)
+        == "StatefulFnComponent must have 'state' as required parameters"
+    )
+
+
+@pytest.mark.asyncio()
+async def test_run_async_step() -> None:
+    """Test run async step."""
+    agent_without_async_fn = FnAgentWorker(
+        fn=mock_foo_fn, asnc_fn=None, initial_state={"max_count": 5}
+    ).as_agent()
+
+    response = await agent_without_async_fn.aquery("hello")
+    assert str(response) == "hello:foo:foo:foo:foo:foo"
+
+    agent_with_async_fn = FnAgentWorker(
+        fn=mock_foo_fn, async_fn=async_mock_foo_fn, initial_state={"max_count": 5}
+    ).as_agent()
+
+    response = await agent_with_async_fn.aquery("hello")
+    assert str(response) == "hello:foo:foo:foo:foo:foo"