Incorrect implementation of ScrollMetrics.extentInside getter  #31430

import 'package:flutter/widgets.dart';
import 'package:test/test.dart';

void main() {
  test('Expect correct extent metrics when max scroll extent is less than viewport dimension', () {

    // Given
    ScrollMetrics metrics = FixedScrollMetrics(
      axisDirection: AxisDirection.down,
      // User scrolled 1 pixel
      pixels: 1,
      // Viewport is 100
      viewportDimension: 100,
      minScrollExtent: 0,
      // User can scroll max 10 pixels
      maxScrollExtent: 10,
    );

    // Extent before is 1, which is correct
    expect(metrics.extentBefore, 1);

    // Extent inside fails here.
    // According to documentation
    // extentInside should be viewport height
    // as extentBefore and extentAfter are non-zero
    // But it is 10, not 100
    expect(metrics.extentInside, 100);

    // Extent after is 9, which is correct
    expect(metrics.extentAfter, 9);
  });
}

[✓] Flutter (Channel stable, v1.2.1, on Linux, locale en_US.UTF-8)