first commit

test/activity_refresh_test.dart

@@ -0,0 +1,47 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import 'package:miler/widget/Bottom_page.dart';
+
+/// The shell keeps every tab alive in an `IndexedStack`: all four pages are
+/// built at launch and switching tabs only changes which one is painted. So a
+/// page that loads in `initState` shows whatever was true before the rider did
+/// anything — which is exactly how a completed stop failed to appear on
+/// Activity. Pages re-read when their index comes forward, so the notifier that
+/// tells them has to actually change.
+void main() {
+  testWidgets('an IndexedStack builds every child up front', (tester) async {
+    final built = <int>[];
+
+    Widget page(int i) => Builder(builder: (_) {
+          built.add(i);
+          return SizedBox(key: ValueKey('page$i'));
+        });
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: IndexedStack(index: 0, children: [page(0), page(1), page(2)]),
+      ),
+    );
+
+    expect(
+      built,
+      containsAll(<int>[0, 1, 2]),
+      reason: 'this is why initState cannot be a page\'s only load',
+    );
+  });
+
+  test('the shell publishes the tab on screen', () {
+    // Starts on Home and is a broadcast point a page can listen to.
+    var heard = <int>[];
+    void listener() => heard.add(BottomPage.currentTab.value);
+
+    BottomPage.currentTab.addListener(listener);
+    addTearDown(() => BottomPage.currentTab.removeListener(listener));
+
+    BottomPage.currentTab.value = 2;
+    BottomPage.currentTab.value = 1;
+
+    expect(heard, [2, 1]);
+  });
+}