diff --git a/swh/core/api/tests/test_serializers.py b/swh/core/api/tests/test_serializers.py
--- a/swh/core/api/tests/test_serializers.py
+++ b/swh/core/api/tests/test_serializers.py
@@ -15,9 +15,9 @@
 from swh.core.api.classes import PagedResult
 from swh.core.api.serializers import (
     ENCODERS,
-    SWHJSONDecoder,
-    SWHJSONEncoder,
     decode_response,
+    json_dumps,
+    json_loads,
     msgpack_dumps,
     msgpack_loads,
 )
@@ -131,33 +131,29 @@
 
 
 def test_serializers_round_trip_json():
-    json_data = json.dumps(DATA, cls=SWHJSONEncoder)
-    actual_data = json.loads(json_data, cls=SWHJSONDecoder)
+    json_data = json_dumps(DATA)
+    actual_data = json_loads(json_data)
     assert actual_data == DATA
 
 
 def test_serializers_round_trip_json_extra_types():
     expected_original_data = [ExtraType("baz", DATA), "qux"]
-    data = json.dumps(
-        expected_original_data, cls=SWHJSONEncoder, extra_encoders=extra_encoders
-    )
-    actual_data = json.loads(data, cls=SWHJSONDecoder, extra_decoders=extra_decoders)
+    data = json_dumps(expected_original_data, extra_encoders=extra_encoders)
+    actual_data = json_loads(data, extra_decoders=extra_decoders)
     assert actual_data == expected_original_data
 
 
 def test_exception_serializer_round_trip_json():
     error_message = "unreachable host"
-    json_data = json.dumps(
-        {"exception": ConnectionError(error_message)}, cls=SWHJSONEncoder
-    )
-    actual_data = json.loads(json_data, cls=SWHJSONDecoder)
+    json_data = json_dumps({"exception": ConnectionError(error_message)},)
+    actual_data = json_loads(json_data)
     assert "exception" in actual_data
     assert type(actual_data["exception"]) == ConnectionError
     assert str(actual_data["exception"]) == error_message
 
 
 def test_serializers_encode_swh_json():
-    json_str = json.dumps(DATA, cls=SWHJSONEncoder)
+    json_str = json_dumps(DATA)
     actual_data = json.loads(json_str)
     assert actual_data == ENCODED_DATA
 
@@ -191,8 +187,8 @@
 
 
 def test_serializers_generator_json():
-    data = json.dumps((i for i in range(5)), cls=SWHJSONEncoder)
-    assert json.loads(data, cls=SWHJSONDecoder) == [i for i in range(5)]
+    data = json_dumps((i for i in range(5)))
+    assert json_loads(data) == [i for i in range(5)]
 
 
 def test_serializers_generator_msgpack():
@@ -237,6 +233,6 @@
 
 
 def test_json_extra_encoders_mutation():
-    data = json.dumps({}, cls=SWHJSONEncoder, extra_encoders=extra_encoders)
+    data = json_dumps({}, extra_encoders=extra_encoders)
     assert data is not None
     assert ENCODERS[-1][0] != ExtraType