diff --git a/swh/storage/tests/algos/test_origin.py b/swh/storage/tests/algos/test_origin.py
--- a/swh/storage/tests/algos/test_origin.py
+++ b/swh/storage/tests/algos/test_origin.py
@@ -16,7 +16,7 @@
 from swh.storage.interface import ListOrder
 from swh.storage.utils import now
 
-from swh.storage.tests.test_storage import round_to_milliseconds
+from swh.storage.tests.storage_tests import round_to_milliseconds
 
 
 def test_iter_origins(swh_storage):
diff --git a/swh/storage/tests/storage_tests.py b/swh/storage/tests/storage_tests.py
--- a/swh/storage/tests/storage_tests.py
+++ b/swh/storage/tests/storage_tests.py
@@ -44,7 +44,7 @@
 from swh.storage.common import origin_url_to_sha1 as sha1
 from swh.storage.exc import HashCollision, StorageArgumentException
 from swh.storage.interface import ListOrder, PagedResult, StorageInterface
-from swh.storage.utils import content_hex_hashes, now
+from swh.storage.utils import content_hex_hashes, now, round_to_milliseconds
 
 
 @contextmanager
@@ -104,23 +104,6 @@
         assert actual_list == expected_list, k
 
 
-def round_to_milliseconds(date):
-    """Round datetime to milliseconds before insertion, so equality doesn't fail after a
-    round-trip through a DB (eg. Cassandra)
-
-    """
-    return date.replace(microsecond=(date.microsecond // 1000) * 1000)
-
-
-def test_round_to_milliseconds():
-    date = now()
-
-    for (ms, expected_ms) in [(0, 0), (1000, 1000), (555555, 555000), (999500, 999000)]:
-        date = date.replace(microsecond=ms)
-        actual_date = round_to_milliseconds(date)
-        assert actual_date.microsecond == expected_ms
-
-
 class LazyContent(Content):
     def with_data(self):
         return Content.from_dict({**self.to_dict(), "data": b"42\n"})
diff --git a/swh/storage/tests/test_api_client.py b/swh/storage/tests/test_api_client.py
--- a/swh/storage/tests/test_api_client.py
+++ b/swh/storage/tests/test_api_client.py
@@ -8,10 +8,10 @@
 import swh.storage.api.server as server
 import swh.storage
 from swh.storage import get_storage
-from swh.storage.tests.test_storage import (
+from swh.storage.tests.storage_tests import (
     TestStorageGeneratedData as _TestStorageGeneratedData,
 )
-from swh.storage.tests.test_storage import TestStorage as _TestStorage
+from swh.storage.tests.storage_tests import TestStorage as _TestStorage
 
 # tests are executed using imported classes (TestStorage and
 # TestStorageGeneratedData) using overloaded swh_storage fixture
diff --git a/swh/storage/tests/test_cassandra.py b/swh/storage/tests/test_cassandra.py
--- a/swh/storage/tests/test_cassandra.py
+++ b/swh/storage/tests/test_cassandra.py
@@ -21,8 +21,8 @@
 from swh.storage.cassandra.model import ContentRow
 
 from swh.storage.utils import now
-from swh.storage.tests.test_storage import TestStorage as _TestStorage
-from swh.storage.tests.test_storage import (
+from swh.storage.tests.storage_tests import TestStorage as _TestStorage
+from swh.storage.tests.storage_tests import (
     TestStorageGeneratedData as _TestStorageGeneratedData,
 )
 
diff --git a/swh/storage/tests/test_utils.py b/swh/storage/tests/test_utils.py
--- a/swh/storage/tests/test_utils.py
+++ b/swh/storage/tests/test_utils.py
@@ -8,6 +8,8 @@
     extract_collision_hash,
     content_hex_hashes,
     content_bytes_hashes,
+    now,
+    round_to_milliseconds,
 )
 
 
@@ -105,3 +107,12 @@
     assert len(actual_content) == len(expected_content)
     for algo in hashutil.DEFAULT_ALGORITHMS:
         assert actual_content[algo] == expected_content[algo]
+
+
+def test_round_to_milliseconds():
+    date = now()
+
+    for (ms, expected_ms) in [(0, 0), (1000, 1000), (555555, 555000), (999500, 999000)]:
+        date = date.replace(microsecond=ms)
+        actual_date = round_to_milliseconds(date)
+        assert actual_date.microsecond == expected_ms
diff --git a/swh/storage/utils.py b/swh/storage/utils.py
--- a/swh/storage/utils.py
+++ b/swh/storage/utils.py
@@ -97,3 +97,11 @@
 
     """
     return {algo: hash_to_bytes(content[algo]) for algo in DEFAULT_ALGORITHMS}
+
+
+def round_to_milliseconds(date):
+    """Round datetime to milliseconds before insertion, so equality doesn't fail after a
+    round-trip through a DB (eg. Cassandra)
+
+    """
+    return date.replace(microsecond=(date.microsecond // 1000) * 1000)