chore: add test for unhandled types

Author: Tom McCarthy

tests/unit/test_json_encoder.py

@@ -1,6 +1,8 @@
 import decimal
 import json
 
+import pytest
+
 from aws_lambda_powertools.shared.json_encoder import Encoder
 
 
@@ -12,3 +14,11 @@ def test_jsonencode_decimal():
 def test_jsonencode_decimal_nan():
     result = json.dumps({"val": decimal.Decimal("NaN")}, cls=Encoder)
     assert result == '{"val": NaN}'
+
+
+def test_jsonencode_calls_default():
+    class CustomClass:
+        pass
+
+    with pytest.raises(TypeError):
+        json.dumps({"val": CustomClass()}, cls=Encoder)