diff --git a/aleph_message/tests/test_utils.py b/aleph_message/tests/test_utils.py
index f9214be..01ae993 100644
--- a/aleph_message/tests/test_utils.py
+++ b/aleph_message/tests/test_utils.py
@@ -1,6 +1,43 @@
-from aleph_message.utils import Gigabytes, gigabyte_to_mebibyte
+from datetime import datetime, date, time
+
+import pytest
+from pydantic import BaseModel
+
+from aleph_message.utils import Gigabytes, gigabyte_to_mebibyte, extended_json_encoder, dump_content
 
 
 def test_gigabyte_to_mebibyte():
     assert gigabyte_to_mebibyte(Gigabytes(1)) == 954
     assert gigabyte_to_mebibyte(Gigabytes(100)) == 95368
+
+
+def test_extended_json_encoder():
+    now = datetime.now()
+    today = date.today()
+    now_time = time(hour=1, minute=2, second=3, microsecond=4)
+    assert extended_json_encoder(now) == now.timestamp()
+    assert extended_json_encoder(today) == today.toordinal()
+    assert extended_json_encoder(now_time) == 3723.000004
+
+
+def test_dump_content():
+    class TestModel(BaseModel):
+        address: str
+        time: float
+
+    assert dump_content({"address": "0x1", "time": 1.0}) == '{"address":"0x1","time":1.0}'
+    assert dump_content(TestModel(address="0x1", time=1.0)) == '{"address":"0x1","time":1.0}'
+
+
+@pytest.mark.parametrize(
+    "content",
+    [
+        1,
+        "test",
+        None,
+        True,
+    ],
+)
+def test_dump_content_invalid(content):
+    with pytest.raises(TypeError):
+        dump_content(content)