diff --git a/swh/journal/tests/test_stream.py b/swh/journal/tests/test_stream.py
new file mode 100644
--- /dev/null
+++ b/swh/journal/tests/test_stream.py
@@ -0,0 +1,47 @@
+# Copyright (C) 2021 The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+import io
+
+import msgpack
+
+from swh.journal.serializers import msgpack_ext_hook
+from swh.journal.writer import get_journal_writer, model_object_dict_sanitizer
+from swh.model.tests.swh_model_data import TEST_OBJECTS
+
+
+def test_write_additions_with_test_objects():
+    outs = io.BytesIO()
+
+    writer = get_journal_writer(
+        cls="stream", value_sanitizer=model_object_dict_sanitizer, output_stream=outs,
+    )
+    expected = []
+
+    n = 0
+    for object_type, objects in TEST_OBJECTS.items():
+        writer.write_additions(object_type, objects)
+
+        for object in objects:
+            objd = object.to_dict()
+            if object_type == "content":
+                objd.pop("data")
+
+            expected.append((object_type, objd))
+        n += len(objects)
+
+    outs.seek(0, 0)
+    unpacker = msgpack.Unpacker(
+        outs,
+        raw=False,
+        ext_hook=msgpack_ext_hook,
+        strict_map_key=False,
+        use_list=False,
+        timestamp=3,  # convert Timestamp in datetime objects (tz UTC)
+    )
+
+    for i, (objtype, objd) in enumerate(unpacker, start=1):
+        assert (objtype, objd) in expected
+    assert len(expected) == i
diff --git a/swh/journal/writer/__init__.py b/swh/journal/writer/__init__.py
--- a/swh/journal/writer/__init__.py
+++ b/swh/journal/writer/__init__.py
@@ -1,4 +1,4 @@
-# Copyright (C) 2019 The Software Heritage developers
+# Copyright (C) 2019-2021 The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
@@ -52,6 +52,10 @@
         from .inmemory import InMemoryJournalWriter as JournalWriter
     elif cls == "kafka":
         from .kafka import KafkaJournalWriter as JournalWriter
+    elif cls == "stream":
+        from .stream import StreamJournalWriter as JournalWriter
+
+        assert "output_stream" in kwargs
     else:
         raise ValueError("Unknown journal writer class `%s`" % cls)
 
diff --git a/swh/journal/writer/inmemory.py b/swh/journal/writer/inmemory.py
--- a/swh/journal/writer/inmemory.py
+++ b/swh/journal/writer/inmemory.py
@@ -5,7 +5,7 @@
 
 import logging
 from multiprocessing import Manager
-from typing import Any, Generic, List, Tuple, TypeVar
+from typing import Any, Callable, Dict, Generic, List, Tuple, TypeVar
 
 from . import ValueProtocol
 
@@ -19,7 +19,9 @@
     objects: List[Tuple[str, TValue]]
     privileged_objects: List[Tuple[str, TValue]]
 
-    def __init__(self, value_sanitizer: Any):
+    def __init__(
+        self, value_sanitizer: Callable[[str, Dict[str, Any]], Dict[str, Any]]
+    ):
         # Share the list of objects across processes, for RemoteAPI tests.
         self.manager = Manager()
         self.objects = self.manager.list()
diff --git a/swh/journal/writer/inmemory.py b/swh/journal/writer/stream.py
copy from swh/journal/writer/inmemory.py
copy to swh/journal/writer/stream.py
--- a/swh/journal/writer/inmemory.py
+++ b/swh/journal/writer/stream.py
@@ -1,11 +1,12 @@
-# Copyright (C) 2019 The Software Heritage developers
+# Copyright (C) 2021 The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 import logging
-from multiprocessing import Manager
-from typing import Any, Generic, List, Tuple, TypeVar
+from typing import Any, BinaryIO, Callable, Dict, Generic, List, TypeVar
+
+from swh.journal.serializers import value_to_kafka
 
 from . import ValueProtocol
 
@@ -15,24 +16,27 @@
 TValue = TypeVar("TValue", bound=ValueProtocol)
 
 
-class InMemoryJournalWriter(Generic[TValue]):
-    objects: List[Tuple[str, TValue]]
-    privileged_objects: List[Tuple[str, TValue]]
+class StreamJournalWriter(Generic[TValue]):
+    """A simple JournalWriter which serializes objects in a stream
+
+    Might be used to serialize a storage in a file to generate a test dataset.
+    """
 
-    def __init__(self, value_sanitizer: Any):
+    def __init__(
+        self,
+        output_stream: BinaryIO,
+        value_sanitizer: Callable[[str, Dict[str, Any]], Dict[str, Any]],
+    ):
         # Share the list of objects across processes, for RemoteAPI tests.
-        self.manager = Manager()
-        self.objects = self.manager.list()
-        self.privileged_objects = self.manager.list()
+        self.output = output_stream
+        self.value_sanitizer = value_sanitizer
 
     def write_addition(
         self, object_type: str, object_: TValue, privileged: bool = False
     ) -> None:
         object_.unique_key()  # Check this does not error, to mimic the kafka writer
-        if privileged:
-            self.privileged_objects.append((object_type, object_))
-        else:
-            self.objects.append((object_type, object_))
+        dict_ = self.value_sanitizer(object_type, object_.to_dict())
+        self.output.write(value_to_kafka((object_type, dict_)))
 
     write_update = write_addition