support for lazy building widgets within viewport

test/core/spatial_hashing_test.dart

@@ -0,0 +1,64 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:infinite_lazy_2d_grid/core/spatial_hashing.dart';
+import 'dart:math';
+import 'package:flutter/material.dart';
+
+void main() {
+  group('SpatialHashing', () {
+    late SpatialHashing<String> spatialHashing;
+
+    setUp(() {
+      spatialHashing = SpatialHashing<String>(cellSize: const Size(10, 10));
+    });
+
+    test('add and retrieve single point', () {
+      final point = Point(5, 5);
+      spatialHashing.add(point, 'A');
+      final results = spatialHashing.getPointsAround(point, const Offset(0, 0));
+      expect(results.length, 1);
+      expect(results.first, (point, 'A'));
+    });
+
+    test('remove point', () {
+      final point = Point(5, 5);
+      spatialHashing.add(point, 'A');
+      spatialHashing.remove(point);
+      final results = spatialHashing.getPointsAround(point, const Offset(0, 0));
+      expect(results, isEmpty);
+    });
+
+    test('add multiple points in same cell', () {
+      final p1 = Point(2, 2);
+      final p2 = Point(7, 7);
+      spatialHashing.add(p1, 'A');
+      spatialHashing.add(p2, 'B');
+      final results = spatialHashing.getPointsAround(p1, const Offset(0, 0));
+      expect(results.length, 2);
+      expect(results, contains((p1, 'A')));
+      expect(results, contains((p2, 'B')));
+    });
+
+    test('add points in different cells and query with offset', () {
+      final p1 = Point(5, 5);
+      final p2 = Point(15, 15);
+      spatialHashing.add(p1, 'A');
+      spatialHashing.add(p2, 'B');
+      // Query with offset to include both cells
+      final results = spatialHashing.getPointsAround(p1, const Offset(10, 10));
+      expect(results.length, 2);
+      expect(results, contains((p1, 'A')));
+      expect(results, contains((p2, 'B')));
+    });
+
+    test('removing one of multiple points in a cell', () {
+      final p1 = Point(2, 2);
+      final p2 = Point(7, 7);
+      spatialHashing.add(p1, 'A');
+      spatialHashing.add(p2, 'B');
+      spatialHashing.remove(p1);
+      final results = spatialHashing.getPointsAround(p2, const Offset(0, 0));
+      expect(results.length, 1);
+      expect(results.first, (p2, 'B'));
+    });
+  });
+}