diff --git a/swh/loader/tests/test_cli.py b/swh/loader/tests/test_cli.py
--- a/swh/loader/tests/test_cli.py
+++ b/swh/loader/tests/test_cli.py
@@ -84,16 +84,19 @@
 
     """
     mock_loader = mocker.patch("swh.loader.cli.get_loader")
+    # mocking because of a discrepancy in behavior between packaged versions
+    mock_iso8601 = mocker.patch("swh.loader.cli.iso8601")
+    parsed_date = datetime.datetime(
+        2016, 5, 3, 15, 16, 32, tzinfo=datetime.timezone.utc
+    )
+    mock_iso8601.parse_date = parsed_date
 
     runner = CliRunner()
     input_date = "2016-05-03 15:16:32+00"
     result = runner.invoke(run, ["npm", "https://some-url", f"visit_date={input_date}"])
     assert result.exit_code == 0
-    expected_parsed_date = datetime.datetime(
-        2016, 5, 3, 15, 16, 32, tzinfo=datetime.timezone.utc
-    )
     mock_loader.assert_called_once_with(
-        "npm", url="https://some-url", visit_date=expected_parsed_date
+        "npm", url="https://some-url", visit_date=parsed_date
     )