Account for the cadence in all the messages

tests/util_test.py

@@ -1,4 +1,6 @@
 import matchy.util as util
+from datetime import datetime, timedelta
+import pytest
 
 
 def test_iterate_all_shifts():
@@ -50,3 +52,51 @@ def test_randomized():
 
     assert util.randomised(string)() == "foo"
     assert util.randomised(list)() in list()
+
+
+@pytest.mark.parametrize(
+    "weekday, hour, start, expected",
+    [
+        pytest.param(
+            0, 0, datetime(2024, 9, 22),
+            datetime(2024, 9, 23), id="tomorrow"
+        ),
+        pytest.param(
+            4, 16, datetime(2024, 9, 22),
+            datetime(2024, 9, 27, 16), id="complicated"
+        ),
+    ],
+)
+def test_get_next_datetime(weekday, hour, start, expected):
+    value = util.get_next_datetime(weekday, hour, start)
+    assert value == expected
+
+
+@pytest.mark.parametrize(
+    "weekday, hour, start, cadence, cadence_start, expected",
+    [
+        pytest.param(
+            0, 0, datetime(2024, 9, 22),
+            1, datetime(2024, 9, 22),
+            datetime(2024, 9, 23), id="tomorrow"
+        ),
+        pytest.param(
+            0, 0, datetime(2024, 9, 22),
+            2, datetime(2024, 9, 22),
+            datetime(2024, 9, 23), id="every-other"
+        ),
+        pytest.param(
+            0, 0, datetime(2024, 9, 22),
+            2, datetime(2024, 9, 14),
+            datetime(2024, 9, 30), id="every-other-before"
+        ),
+        pytest.param(
+            0, 0, datetime(2024, 9, 22),
+            3, datetime(2024, 9, 14),
+            datetime(2024, 10, 7), id="every-third"
+        ),
+    ],
+)
+def test_get_next_datetime_with_cadence(weekday, hour, start, expected, cadence, cadence_start):
+    value = util.get_next_datetime_with_cadence(weekday, hour, start, cadence, cadence_start)
+    assert value == expected