diff --git a/app/scodoc/sco_utils.py b/app/scodoc/sco_utils.py
index 53d2c66cb..c2f6f2dde 100644
--- a/app/scodoc/sco_utils.py
+++ b/app/scodoc/sco_utils.py
@@ -152,16 +152,20 @@ def convert_fr_date(
     raise ScoValueError("Date (j/m/a) invalide")
 
 
-def heure_to_iso8601(t, null_is_empty=False) -> str:
-    "convert time string to ISO 8601 (allow 16:03, 16h03, 16)"
+def heure_to_iso8601(t: str | datetime.time = None) -> str:
+    """Convert time string or time object to ISO 8601 (allows 16:03, 16h03, 16),
+    returns hh:mm:ss or empty string
+    """
     if isinstance(t, datetime.time):
         return t.isoformat()
-    if not t and null_is_empty:
+    if not t:
         return ""
-    t = t.strip().upper().replace("H", ":")
-    if t and t.count(":") == 0 and len(t) < 3:
-        t = t + ":00"
-    return t
+    parts = t.strip().upper().replace("H", ":").split(":")
+    # here we can have hh, hh:mm or hh:mm:ss
+    h = int(parts[0])
+    m = int(parts[1]) if len(parts) > 1 else 0
+    s = int(parts[2]) if len(parts) > 2 else 0
+    return datetime.time(h, m, s).isoformat()
 
 
 def print_progress_bar(
diff --git a/tests/unit/test_sco_utils.py b/tests/unit/test_sco_utils.py
new file mode 100644
index 000000000..4f0baa16d
--- /dev/null
+++ b/tests/unit/test_sco_utils.py
@@ -0,0 +1,82 @@
+"""Test des fonctions utilitaires de sco_utils.py
+
+
+Utiliser comme:
+    pytest tests/unit/test_sco_utils.py
+
+"""
+
+# pylint: disable=C0111
+# no doc strings in short tests
+
+import datetime
+import pytest
+
+from app.scodoc.sco_exceptions import ScoValueError
+from app.scodoc.sco_utils import convert_fr_date, heure_to_iso8601
+
+
+def test_convert_fr_date_full_date():
+    assert convert_fr_date("12/2/1972") == datetime.datetime(1972, 2, 12)
+
+
+def test_convert_fr_date_short_date_before_pivot():
+    assert convert_fr_date("12/2/24") == datetime.datetime(2024, 2, 12)
+
+
+def test_convert_fr_date_short_date_after_pivot():
+    assert convert_fr_date("12/2/72") == datetime.datetime(1972, 2, 12)
+
+
+def test_convert_fr_date_datetime_object():
+    dt = datetime.datetime(2022, 2, 12)
+    assert convert_fr_date(dt) == dt
+
+
+def test_convert_fr_date_invalid_date():
+    with pytest.raises(ScoValueError):
+        convert_fr_date("invalid date")
+
+
+def test_convert_fr_date_iso_format():
+    assert convert_fr_date("2022-02-12T00:00:00") == datetime.datetime(2022, 2, 12)
+
+
+def test_convert_fr_date_invalid_iso_format():
+    with pytest.raises(ScoValueError):
+        convert_fr_date("2022-02-30T00:00:00")
+
+
+def test_heure_to_iso8601_full_time():
+    assert heure_to_iso8601("16:01:02") == "16:01:02"
+
+
+def test_heure_to_iso8601_hour_minute():
+    assert heure_to_iso8601("16:03") == "16:03:00"
+
+
+def test_heure_to_iso8601_hour_only():
+    assert heure_to_iso8601("16") == "16:00:00"
+
+
+def test_heure_to_iso8601_single_digit():
+    assert heure_to_iso8601("1:2:3") == "01:02:03"
+
+
+def test_heure_to_iso8601_invalid_input():
+    with pytest.raises(ValueError):
+        heure_to_iso8601("invalid")
+
+
+def test_heure_to_iso8601_datetime_time():
+    time_obj = datetime.time(16, 1, 2)
+    assert heure_to_iso8601(time_obj) == "16:01:02"
+
+
+def test_heure_to_iso8601_null():
+    assert heure_to_iso8601("") == ""
+
+
+# Run the tests
+if __name__ == "__main__":
+    pytest.main()