anchor.diff:      expect(rail.size.width, equals(300.0));
     });
   
  +  /// Regression test for https://github.com/flutter/flutter/issues/65657
     testWidgets('Extended rail transition does not jump from the beginning', (WidgetTester tester) async {
       bool extended = false;
       StateSetter stateSetter;
  
positive.code:       ),
      );
  
      final RenderBox rail = tester.firstRenderObject<RenderBox>(find.byType(NavigationRail));
  
      expect(rail.size.width, equals(72.0));
  
      stateSetter(() {
        extended = true;
  
negative.code:     // Create very close to 0, but non-zero, animation value.
      await tester.pump(const Duration(milliseconds: 1));
      // Expect that it has started to extend.
      expect(tester.getSize(rail).width, greaterThan(72.0));
      // Expect that it has only extended by a small amount, or that the first
      // frame does not jump. This helps verify that it is a smooth animation.
      expect(tester.getSize(rail).width, closeTo(72.0, 1.0));
    });
  
    testWidgets('Extended rail animation can be consumed', (WidgetTester tester) async {
  