diff --git a/swh/journal/tests/conftest.py b/swh/journal/tests/conftest.py
--- a/swh/journal/tests/conftest.py
+++ b/swh/journal/tests/conftest.py
@@ -3,6 +3,7 @@
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
+import datetime
 import os
 import pytest
 import logging
@@ -28,6 +29,9 @@
 from swh.model.hashutil import MultiHash, hash_to_bytes
 
 
+from swh.journal.writer.kafka import OBJECT_TYPES, ModelObject
+
+
 logger = logging.getLogger(__name__)
 
 CONTENTS = [
@@ -149,6 +153,24 @@
     "origin_visit": (None, ORIGIN_VISITS),
 }
 
+MODEL_OBJECTS = {v: k for (k, v) in OBJECT_TYPES.items()}
+
+TEST_OBJECTS: Dict[str, List[ModelObject]] = {}
+
+for object_type, (_, objects) in TEST_OBJECT_DICTS.items():
+    converted_objects: List[ModelObject] = []
+    model = MODEL_OBJECTS[object_type]
+
+    for (num, obj_d) in enumerate(objects):
+        if object_type == "origin_visit":
+            obj_d = {**obj_d, "visit": num}
+        elif object_type == "content":
+            obj_d = {**obj_d, "data": b"", "ctime": datetime.datetime.now()}
+
+        converted_objects.append(model.from_dict(obj_d))
+
+    TEST_OBJECTS[object_type] = converted_objects
+
 
 KAFKA_ROOT = os.environ.get("SWH_KAFKA_ROOT")
 KAFKA_ROOT = KAFKA_ROOT if KAFKA_ROOT else os.path.dirname(__file__) + "/kafka"
diff --git a/swh/journal/tests/test_kafka_writer.py b/swh/journal/tests/test_kafka_writer.py
--- a/swh/journal/tests/test_kafka_writer.py
+++ b/swh/journal/tests/test_kafka_writer.py
@@ -4,23 +4,19 @@
 # See top-level LICENSE file for more information
 
 from collections import defaultdict
-import datetime
 
 from confluent_kafka import Consumer, KafkaException
 from subprocess import Popen
-from typing import List, Tuple
+from typing import Tuple
 
 from swh.storage import get_storage
 
-from swh.journal.replay import object_converter_fn
 from swh.journal.serializers import kafka_to_key, kafka_to_value
-from swh.journal.writer.kafka import KafkaJournalWriter, OBJECT_TYPES
+from swh.journal.writer.kafka import KafkaJournalWriter
 
-from swh.model.model import Content, Origin, BaseModel
+from swh.model.model import Origin, OriginVisit
 
-from .conftest import TEST_OBJECT_DICTS
-
-MODEL_OBJECTS = {v: k for (k, v) in OBJECT_TYPES.items()}
+from .conftest import TEST_OBJECTS, TEST_OBJECT_DICTS
 
 
 def consume_messages(consumer, kafka_prefix, expected_messages):
@@ -93,16 +89,9 @@
 
     expected_messages = 0
 
-    for (object_type, (_, objects)) in TEST_OBJECT_DICTS.items():
-        for (num, object_d) in enumerate(objects):
-            if object_type == "origin_visit":
-                object_d = {**object_d, "visit": num}
-            if object_type == "content":
-                object_d = {**object_d, "ctime": datetime.datetime.now()}
-            object_ = MODEL_OBJECTS[object_type].from_dict(object_d)
-
-            writer.write_addition(object_type, object_)
-            expected_messages += 1
+    for object_type, objects in TEST_OBJECTS.items():
+        writer.write_additions(object_type, objects)
+        expected_messages += len(objects)
 
     consumed_messages = consume_messages(consumer, kafka_prefix, expected_messages)
     assert_all_objects_consumed(consumed_messages)
@@ -128,7 +117,7 @@
 
     expected_messages = 0
 
-    for (object_type, (_, objects)) in TEST_OBJECT_DICTS.items():
+    for object_type, objects in TEST_OBJECTS.items():
         method = getattr(storage, object_type + "_add")
         if object_type in (
             "content",
@@ -138,23 +127,19 @@
             "snapshot",
             "origin",
         ):
-            objects_: List[BaseModel]
-            if object_type == "content":
-                objects_ = [Content.from_dict({**obj, "data": b""}) for obj in objects]
-            else:
-                objects_ = [object_converter_fn[object_type](obj) for obj in objects]
-            method(objects_)
+            method(objects)
             expected_messages += len(objects)
         elif object_type in ("origin_visit",):
-            for object_ in objects:
-                object_ = object_.copy()
-                origin_url = object_.pop("origin")
-                storage.origin_add_one(Origin(url=origin_url))
-                visit = method(
-                    origin_url, date=object_.pop("date"), type=object_.pop("type")
-                )
+            for obj in objects:
+                assert isinstance(obj, OriginVisit)
+                storage.origin_add_one(Origin(url=obj.origin))
+                visit = method(obj.origin, date=obj.date, type=obj.type)
                 expected_messages += 1
-                storage.origin_visit_update(origin_url, visit.visit, **object_)
+
+                obj_d = obj.to_dict()
+                for k in ("visit", "origin", "date", "type"):
+                    del obj_d[k]
+                storage.origin_visit_update(obj.origin, visit.visit, **obj_d)
                 expected_messages += 1
         else:
             assert False, object_type
diff --git a/swh/journal/writer/kafka.py b/swh/journal/writer/kafka.py
--- a/swh/journal/writer/kafka.py
+++ b/swh/journal/writer/kafka.py
@@ -153,6 +153,8 @@
         if object_type == "origin_visit":
             # :(
             dict_["date"] = str(dict_["date"])
+        if object_type == "content":
+            dict_.pop("data", None)
         return dict_
 
     def _write_addition(self, object_type: str, object_: ModelObject) -> None: