Add tests for string serializer (#996)

Co-authored-by: openhands <openhands@all-hands.dev>

Author: enyst

openhands-sdk/openhands/sdk/llm/utils/model_features.py

@@ -89,10 +89,13 @@ class ModelFeatures:
 # Models that require string serializer for tool messages
 # These models don't support structured content format [{"type":"text","text":"..."}]
 # and need plain strings instead
+# NOTE: model_matches uses case-insensitive substring matching, not globbing.
+#       Keep these entries as bare substrings without wildcards.
 FORCE_STRING_SERIALIZER_PATTERNS: list[str] = [
-    "deepseek",
-    "glm",
-    "groq/kimi-k2-instruct",
+    "deepseek",  # e.g., DeepSeek-V3.2-Exp
+    "glm",  # e.g., GLM-4.5 / GLM-4.6
+    # Kimi K2-Instruct requires string serialization only on Groq
+    "groq/kimi-k2-instruct",  # explicit provider-prefixed IDs
 ]
 
 

tests/sdk/llm/test_model_features.py

@@ -226,3 +226,17 @@ def test_supports_stop_words_false_models(model):
 def test_responses_api_support(model, expected_responses):
     features = get_features(model)
     assert features.supports_responses_api is expected_responses
+
+
+def test_force_string_serializer_full_model_names():
+    """Ensure full model names match substring patterns for string serializer.
+
+    Regression coverage for patterns like deepseek/glm without wildcards; Kimi
+    should only match when provider-prefixed with groq/.
+    """
+    assert get_features("DeepSeek-V3.2-Exp").force_string_serializer is True
+    assert get_features("GLM-4.5").force_string_serializer is True
+    # Provider-agnostic Kimi should not force string serializer
+    assert get_features("Kimi K2-Instruct-0905").force_string_serializer is False
+    # Groq-prefixed Kimi should force string serializer
+    assert get_features("groq/kimi-k2-instruct-0905").force_string_serializer is True