Add a test for public and private computes

This fails for now.

tests/test_reactive.py

@@ -435,3 +435,27 @@ async def test_public_and_private_validate() -> None:
         pilot.app.counter += 1
         assert calls["private"] is True
         assert calls["public"] is True
+
+
+async def test_public_and_private_compute() -> None:
+    """If a reactive/var has public and private compute both should get called."""
+
+    calls: dict[str, bool] = {"private": False, "public": False}
+
+    class PrivateComputeTest(App):
+        counter = var(0, init=False)
+
+        def compute_counter(self) -> int:
+            calls["public"] = True
+            return 23
+
+        def _compute_counter(self) -> int:
+            calls["private"] = True
+            return 42
+
+    async with PrivateComputeTest().run_test() as pilot:
+        assert calls["private"] is False
+        assert calls["public"] is False
+        _ = pilot.app.counter
+        assert calls["private"] is True
+        assert calls["public"] is True