[Material] Unit test for skipping Slider tick mark due to overdensity

packages/flutter/lib/src/material/slider.dart

@@ -1005,16 +1005,16 @@ class _RenderSlider extends RenderBox {
         isEnabled: isInteractive,
         sliderTheme: _sliderTheme,
       ).width;
-      // If the ticks would be too dense, don't bother painting them.
-      if ((trackRect.width - tickMarkWidth) / divisions >= 3.0 * tickMarkWidth) {
+      final double adjustedTrackWidth = trackRect.width - tickMarkWidth;
+      // If the tick marks would be too dense, don't bother painting them.
+      if (adjustedTrackWidth / divisions >= 3.0 * tickMarkWidth) {
+        final double dy = trackRect.center.dy;
         for (int i = 0; i <= divisions; i++) {
-          final double tickValue = i / divisions;
+          final double value = i / divisions;
           // The ticks are mapped to be within the track, so the tick mark width
           // must be subtracted from the track width.
-          final double tickX = trackRect.left +
-              tickValue * (trackRect.width - tickMarkWidth) + tickMarkWidth / 2;
-          final double tickY = trackRect.center.dy;
-          final Offset tickMarkOffset = Offset(tickX, tickY);
+          final double dx = trackRect.left + value * adjustedTrackWidth + tickMarkWidth / 2;
+          final Offset tickMarkOffset = Offset(dx, dy);
           _sliderTheme.tickMarkShape.paint(
             context,
             tickMarkOffset,

packages/flutter/test/material/slider_test.dart

@@ -978,6 +978,63 @@ void main() {
     await tester.pumpAndSettle();
   });
 
+  testWidgets('Tick marks are skipped when they aro too dense', (WidgetTester tester) async {
+    double value = 25.0;
+
+    Widget buildSlider({
+      int divisions,
+      TextDirection textDirection,
+    }) {
+      return Directionality(
+        textDirection: textDirection,
+        child: StatefulBuilder(
+          builder: (BuildContext context, StateSetter setState) {
+            return MediaQuery(
+              data: MediaQueryData.fromWindow(window),
+              child: Material(
+                child: Center(
+                  child: Slider(
+                    min: 0.0,
+                    max: 100.0,
+                    divisions: divisions,
+                    value: value,
+                    onChanged: (double newValue) {
+                      setState(() {
+                        value = newValue;
+                      });
+                    },
+                  ),
+                ),
+              ),
+            );
+          },
+        ),
+      );
+    }
+
+    await tester.pumpWidget(
+      buildSlider(
+        textDirection: TextDirection.ltr,
+        divisions: 4,
+      ),
+    );
+
+    final RenderBox sliderBox = tester.firstRenderObject<RenderBox>(find.byType(Slider));
+
+    // 5 tick marks and a thumb.
+    expect(sliderBox, paintsExactlyCountTimes(#drawCircle, 6));
+
+    await tester.pumpWidget(
+      buildSlider(
+        textDirection: TextDirection.ltr,
+        divisions: 500,
+      ),
+    );
+
+    // No tick marks because they are too dense, just a thumb.
+    expect(sliderBox, paintsExactlyCountTimes(#drawCircle, 1));
+  });
+
   testWidgets('Slider has correct animations when reparented', (WidgetTester tester) async {
     final Key sliderKey = GlobalKey(debugLabel: 'A');
     double value = 0.0;