tests: basic workspace tree functions

tests/test_ui/test_workspace_tree.py

@@ -0,0 +1,23 @@
+from tests.test_ui.ui_base import run_pilot
+from dooit.ui.tui import Dooit
+
+
+async def workspaces_tree():
+    async with run_pilot() as pilot:
+        app = pilot.app
+        assert isinstance(app, Dooit)
+
+        wtree = app.workspace_tree
+
+        assert len(wtree._options) == 0
+
+        wtree.add_workspace()
+        wtree.add_workspace()
+        wtree.add_workspace()
+        w = wtree.add_workspace()
+
+        assert len(wtree._options) == 4
+
+        wtree.highlight_id(w)
+
+        assert wtree.highlighted == 3  # n-1