diff --git a/domain/abri/slots.py b/domain/abri/slots.py
new file mode 100644
index 000000000..1f777f5ca
--- /dev/null
+++ b/domain/abri/slots.py
@@ -0,0 +1,7 @@
+from typing import Optional
+
+from domain.abri.models import SlotCode
+
+
+def slot_for_confirmed_time(confirmed_time: Optional[str]) -> SlotCode:
+    raise NotImplementedError
diff --git a/tests/domain/abri/__init__.py b/tests/domain/abri/__init__.py
new file mode 100644
index 000000000..e69de29bb
diff --git a/tests/domain/abri/test_slots.py b/tests/domain/abri/test_slots.py
new file mode 100644
index 000000000..3b587064e
--- /dev/null
+++ b/tests/domain/abri/test_slots.py
@@ -0,0 +1,16 @@
+from typing import Optional
+
+import pytest
+
+from domain.abri.slots import slot_for_confirmed_time
+
+
+@pytest.mark.parametrize("confirmed_time", [None, "", "   "])
+def test_a_booking_with_no_confirmed_time_is_an_all_day_appointment(
+    confirmed_time: Optional[str],
+) -> None:
+    # Act
+    slot = slot_for_confirmed_time(confirmed_time)
+
+    # Assert
+    assert slot == "AD"