Start unit tests for the actual selected property

tests/selection_list/test_selection_values.py

@@ -0,0 +1,72 @@
+"""Unit tests dealing with the tracking of selection list values."""
+
+from __future__ import annotations
+
+from textual.app import App, ComposeResult
+from textual.widgets import SelectionList
+
+
+class SelectionListApp(App[None]):
+    def __init__(self, default_state: bool = False) -> None:
+        super().__init__()
+        self._default_state = default_state
+
+    def compose(self) -> ComposeResult:
+        yield SelectionList[int](*[(str(n), n, self._default_state) for n in range(50)])
+
+
+async def test_empty_selected() -> None:
+    """Selected should be empty when nothing is selected."""
+    async with SelectionListApp().run_test() as pilot:
+        assert pilot.app.query_one(SelectionList).selected == []
+
+
+async def test_programatic_select() -> None:
+    """Selected should contain a selected value."""
+    async with SelectionListApp().run_test() as pilot:
+        selection = pilot.app.query_one(SelectionList)
+        selection.select(0)
+        assert pilot.app.query_one(SelectionList).selected == [0]
+
+
+async def test_programatic_select_all() -> None:
+    """Selected should contain all selected values."""
+    async with SelectionListApp().run_test() as pilot:
+        selection = pilot.app.query_one(SelectionList)
+        selection.select_all()
+        assert pilot.app.query_one(SelectionList).selected == list(range(50))
+
+
+async def test_programatic_deselect() -> None:
+    """Selected should not contain a deselected value."""
+    async with SelectionListApp(True).run_test() as pilot:
+        selection = pilot.app.query_one(SelectionList)
+        selection.deselect(0)
+        assert pilot.app.query_one(SelectionList).selected == list(range(50)[1:])
+
+
+async def test_programatic_deselect_all() -> None:
+    """Selected should not contain anything after deselecting all values."""
+    async with SelectionListApp(True).run_test() as pilot:
+        selection = pilot.app.query_one(SelectionList)
+        selection.deselect_all()
+        assert pilot.app.query_one(SelectionList).selected == []
+
+
+async def test_programatic_toggle() -> None:
+    """Selected should reflect a toggle."""
+    async with SelectionListApp().run_test() as pilot:
+        selection = pilot.app.query_one(SelectionList)
+        for n in range(25, 50):
+            selection.select(n)
+        for n in range(50):
+            selection.toggle(n)
+        assert pilot.app.query_one(SelectionList).selected == list(range(50)[:25])
+
+
+async def test_programatic_toggle_all() -> None:
+    """Selected should contain all values after toggling all on."""
+    async with SelectionListApp().run_test() as pilot:
+        selection = pilot.app.query_one(SelectionList)
+        selection.toggle_all()
+        assert pilot.app.query_one(SelectionList).selected == list(range(50))