refactor: rely on platform scroll physics and add scroll behavior tests

2026-09-18 17:01:17 +05:30
parent 5122eebc11
commit 4adc21a277
3 changed files with 110 additions and 18 deletions
--- a/test/scroll_behaviour_test.dart
+++ b/test/scroll_behaviour_test.dart
@@ -0,0 +1,91 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:krow_worker_app/main.dart';
+
+/// A list whose content is shorter than the viewport, so there is nothing to
+/// scroll to.
+Widget shortList() => MaterialApp(
+  scrollBehavior: const KrowScrollBehavior(),
+  home: Scaffold(
+    body: ListView(
+      children: const [SizedBox(height: 100, child: Text('only item'))],
+    ),
+  ),
+);
+
+Widget longList() => MaterialApp(
+  scrollBehavior: const KrowScrollBehavior(),
+  home: Scaffold(
+    body: ListView(
+      children: [
+        for (var i = 0; i < 40; i++) SizedBox(height: 100, child: Text('$i')),
+      ],
+    ),
+  ),
+);
+
+ScrollPosition positionOf(WidgetTester tester) =>
+    tester.state<ScrollableState>(find.byType(Scrollable)).position;
+
+void main() {
+  // TargetPlatformVariant sets and restores the override around each test;
+  // assigning it by hand trips the framework's debug-variable invariant check.
+  final android = TargetPlatformVariant.only(TargetPlatform.android);
+  final ios = TargetPlatformVariant.only(TargetPlatform.iOS);
+
+  group('on Android', () {
+    testWidgets('content that already fits does not move when dragged', (
+      tester,
+    ) async {
+      await tester.pumpWidget(shortList());
+      final position = positionOf(tester);
+
+      // Every vertical list without a controller is handed an
+      // AlwaysScrollableScrollPhysics by ScrollView itself, so the drag is
+      // accepted whatever the content. Clamping is what pins it to the
+      // boundary. Forcing bouncing globally instead let a one-item list be
+      // dragged hundreds of pixels down, leaving a gap under the header.
+      await tester.drag(find.text('only item'), const Offset(0, 300));
+      await tester.pump();
+
+      expect(position.pixels, 0);
+    }, variant: android);
+
+    testWidgets('a list that overflows still scrolls', (tester) async {
+      await tester.pumpWidget(longList());
+      final position = positionOf(tester);
+
+      await tester.drag(find.text('0'), const Offset(0, -200));
+      await tester.pump();
+
+      expect(position.pixels, greaterThan(0));
+    }, variant: android);
+
+    testWidgets('and does not overscroll past the top', (tester) async {
+      await tester.pumpWidget(longList());
+      final position = positionOf(tester);
+
+      await tester.drag(find.byType(Scrollable), const Offset(0, 400));
+      await tester.pump();
+
+      expect(position.pixels, 0);
+    }, variant: android);
+  });
+
+  group('on iOS', () {
+    testWidgets('short content rubber-bands, which is the convention there', (
+      tester,
+    ) async {
+      await tester.pumpWidget(shortList());
+      final position = positionOf(tester);
+
+      await tester.drag(find.text('only item'), const Offset(0, 300));
+      await tester.pump();
+      expect(position.pixels, lessThan(0));
+
+      // And springs back on release, rather than leaving the gap behind.
+      await tester.pumpAndSettle();
+      expect(position.pixels, 0);
+    }, variant: ios);
+  });
+}