Hi @QuncCccccc and @dkwingsmt. Thanks a lot for your reviews!

Regarding the change from divisions: 3 to divisions: 5. The lower division count was causing an unintentional snapping behavior during the test, which triggered additional painting logic.

When divisions: 3 is used, the initial thumb positions do not align perfectly with the discrete divisions. As soon as the test interacts with the slider, the thumbs snap to the nearest division to stay consistent with the discrete intervals.

Once the snap occurs, the thumbs overlap at the same value, and the top thumb receives a white border.

Previously, _handleDragStart and _handleDragEnd did not trigger a setState. With the changes in this PR, a setState is correctly called, which causes the framework to paint that white border.

The paints matcher in the test expects a specific sequence of draw calls.

expect(
  valueIndicatorBox,
  paints
    // Represents the raised button wth next text.
    ..path(color: Colors.black)
    ..paragraph()
    // Represents the range slider.
    ..path(color: fillColor)
    ..paragraph()
    ..path(color: fillColor)
    ..paragraph(),
);

Because of the white border, the actual paint sequence includes an extra ..path(color: Colors.white) that the test wasn't expecting:

Expected sequence (with divisions: 3):

expect(
  valueIndicatorBox,
  paints
    ..path(color: Colors.black) // Button
    ..paragraph()
    ..path(color: fillColor)   // Thumb Path 1
    ..paragraph()
    ..path(color: Colors.white) // <--- The white border path causing the mismatch
    ..path(color: fillColor)   // Thumb Path 2
    ..paragraph(),
);

By switching to divisions: 5, the initial thumb values align perfectly with the discrete steps from the start. This prevents the thumbs' realignment during the first interaction, meaning the white border is never painted, and the original paint expectations remain valid.

@QuncCccccc thanks a lot for your review!