Add some basic unit tests

QuadtreeTests/Tests.cs

@@ -1,19 +1,74 @@
+using NSubstitute;
 using SpatialCollections;
+using System.Numerics;
 
 namespace QuadtreeTests
 {
     public class Tests
     {
+        private class TestWorldObject(Vector2 position) : IWorldObject
+        {
+            public Vector2 Position { get; } = position;
+
+            public float BoundingRadius { get; } = 1.0f;
+
+            public BoundingBox2 BoundingBox { get; } = new BoundingBox2(position - Vector2.One, position + Vector2.One);
+        }
+
+        private List<Vector2> _positions;
+
+        private List<IWorldObject> _objects;
+
+        private Quadtree _quadtree;
+
         [SetUp]
         public void Setup()
         {
+            _positions = [new Vector2(1.0f, 1.0f), new Vector2(3.0f, 3.0f), new Vector2(5.0f, 8.0f)];
+            _objects = new();
+            _quadtree = new(20, 4);
+
+            for (int i = 0; i < _positions.Count; i++)
+            {
+                var obj = new TestWorldObject(_positions[i]);
+                _objects.Add(obj);
+            }
         }
 
         [Test]
-        public void Test1()
+        public void TestAdd()
         {
-            Quadtree quadtree = new(20, 4);
-            Assert.Pass();
+            AddObjectsAndAssertCount();
+        }
+
+        [Test]
+        public void TestAddRemove()
+        {
+            AddObjectsAndAssertCount();
+
+            for (int i = 0; i < _objects.Count; i++)
+            {
+                _quadtree.Remove(_objects[i]);
+                Assert.That(_quadtree.Count, Is.EqualTo(_objects.Count - i - 1));
+            }
+        }
+
+        [Test]
+        public void TestQuery()
+        {
+            AddObjectsAndAssertCount();
+            List<IWorldObject> result = new();
+            _quadtree.Query(new BoundingBox2(new Vector2(3.5f, 3.5f), new Vector2(10.0f, 10.0f)), result);
+            Assert.That(result.Count, Is.EqualTo(2));
+        }
+
+        private void AddObjectsAndAssertCount()
+        {
+            for (int i = 0; i < _objects.Count; i++)
+            {
+                _quadtree.Add(_objects[i]);
+                Assert.That(_quadtree.Count, Is.EqualTo(i + 1));
+            }
         }
     }
 }