Fix JsonSerializer returning None and raising TypeError on deserialize

kafka/serializer/json.py

@@ -1,9 +1,9 @@
 import json
 
-from .abstract import Serializer, Deserializer
+from .default import DefaultSerializer
 
 
-class JsonSerializer(Serializer, Deserializer):
+class JsonSerializer(DefaultSerializer):
     def serialize(self, topic, headers, data):
         if data is None:
             return None

test/test_serializer.py

@@ -0,0 +1,47 @@
+# pylint: skip-file
+
+import pytest
+
+from kafka.serializer import DefaultSerializer, JsonSerializer
+
+
+@pytest.mark.parametrize('encoding', ['utf-8', 'utf-16'])
+def test_default_serializer_roundtrip(encoding):
+    ser = DefaultSerializer(encoding)
+    data = 'h\u00e9llo w\u00f6rld'
+    encoded = ser.serialize('topic', [], data)
+    assert isinstance(encoded, bytes)
+    assert ser.deserialize('topic', [], encoded) == data
+
+
+@pytest.mark.parametrize('data', [b'raw', bytearray(b'raw'), memoryview(b'raw'), None])
+def test_default_serializer_passthrough_bytes_like(data):
+    assert DefaultSerializer().serialize('topic', [], data) == data
+
+
+def test_default_serializer_deserialize_none():
+    assert DefaultSerializer().deserialize('topic', [], None) is None
+
+
+def test_default_serializer_rejects_non_bytes_str():
+    with pytest.raises(AttributeError):
+        DefaultSerializer().serialize('topic', [], 42)
+
+
+def test_json_serializer_roundtrip():
+    ser = JsonSerializer()
+    data = {'key': 'value', 'n': 42, 'lst': [1, 2]}
+    encoded = ser.serialize('topic', [], data)
+    assert isinstance(encoded, bytes)
+    assert ser.deserialize('topic', [], encoded) == data
+
+
+def test_json_serializer_none():
+    ser = JsonSerializer()
+    assert ser.serialize('topic', [], None) is None
+    assert ser.deserialize('topic', [], None) is None
+
+
+def test_json_serializer_deserializes_plain_json():
+    ser = JsonSerializer()
+    assert ser.deserialize('topic', [], b'{"a": 1}') == {'a': 1}