Add to_iso8601() tests

Author: maddenp-cu

src/uwtools/tests/utils/test_time.py

@@ -4,6 +4,8 @@
 
 from datetime import timedelta
 
+from pytest import mark
+
 from uwtools.utils import time
 
 
@@ -13,6 +15,17 @@ def test_utils_time_to_datetime(utc):
         assert time.to_datetime(value=value) == expected
 
 
+@mark.parametrize("sep", ["T", " "])
+@mark.parametrize("val", ["2025-07-31%s12", "2025-07-31%s12:00", "2025-07-31%s12:00:00"])
+def test_utils_time_to_iso8601(sep, val):
+    assert time.to_iso8601(val % sep) == "2025-07-31T12:00:00"
+
+
+def test_utils_time_to_iso8601_dtobj(utc):
+    dtobj = utc(2025, 7, 31, 12)
+    assert time.to_iso8601(dtobj) == "2025-07-31T12:00:00"
+
+
 def test_utils_time_to_timedelta():
     for value, expected in [
         ("01:02:03", timedelta(hours=1, minutes=2, seconds=3)),