style: add return type annotations to new test methods

Author: enjoykumawat

tests/unittests/a2a/converters/test_from_adk.py

@@ -111,44 +111,44 @@ def test_convert_event_to_a2a_events_none_artifacts(self):
 class TestSerializeValue:
   """Tests for _serialize_value preserving JSON-native types."""
 
-  def setup_method(self):
+  def setup_method(self) -> None:
     from google.adk.a2a.converters.from_adk_event import _serialize_value
 
     self.serialize = _serialize_value
 
-  def test_dict_preserved(self):
+  def test_dict_preserved(self) -> None:
     value = {"key": "val", "nested": {"a": 1}}
     result = self.serialize(value)
     assert result == value
     assert isinstance(result, dict)
 
-  def test_list_preserved(self):
+  def test_list_preserved(self) -> None:
     value = [1, "two", {"three": 3}]
     result = self.serialize(value)
     assert result == value
     assert isinstance(result, list)
 
-  def test_int_preserved(self):
+  def test_int_preserved(self) -> None:
     result = self.serialize(42)
     assert result == 42
     assert isinstance(result, int)
 
-  def test_float_preserved(self):
+  def test_float_preserved(self) -> None:
     result = self.serialize(3.14)
     assert result == 3.14
     assert isinstance(result, float)
 
-  def test_bool_preserved(self):
+  def test_bool_preserved(self) -> None:
     assert self.serialize(True) is True
     assert self.serialize(False) is False
 
-  def test_string_preserved(self):
+  def test_string_preserved(self) -> None:
     assert self.serialize("hello") == "hello"
 
-  def test_none_returns_none(self):
+  def test_none_returns_none(self) -> None:
     assert self.serialize(None) is None
 
-  def test_non_json_type_stringified(self):
+  def test_non_json_type_stringified(self) -> None:
     """Non-JSON-native types should still be converted to str."""
     from datetime import datetime