Add tests for ClosestBeatDivisor

Used https://github.com/ppy/osu/pull/12558/files#diff-5c1f04c5b262ca3abbaf867aa91b62a60b66691323c286ad5aa0b75c153cc6ca as reference.

osu.Game.Tests/NonVisual/ClosestBeatDivisorTest.cs

@@ -0,0 +1,91 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System.Collections.Generic;
+using NUnit.Framework;
+using osu.Game.Beatmaps;
+using osu.Game.Beatmaps.ControlPoints;
+using osu.Game.Rulesets.Objects;
+
+namespace osu.Game.Tests.NonVisual
+{
+    public class ClosestBeatDivisorTest
+    {
+        [Test]
+        public void TestExactDivisors()
+        {
+            var cpi = new ControlPointInfo();
+            cpi.Add(-1000, new TimingControlPoint { BeatLength = 1000 });
+
+            double[] divisors = { 3, 1, 16, 12, 8, 6, 4, 3, 2, 1 };
+
+            assertClosestDivisors(divisors, divisors, cpi);
+        }
+
+        [Test]
+        public void TestExactDivisorWithTempoChanges()
+        {
+            int offset = 0;
+            int[] beatLengths = { 1000, 200, 100, 50 };
+
+            var cpi = new ControlPointInfo();
+
+            foreach (int beatLength in beatLengths)
+            {
+                cpi.Add(offset, new TimingControlPoint { BeatLength = beatLength });
+                offset += beatLength * 2;
+            }
+
+            double[] divisors = { 3, 1, 16, 12, 8, 6, 4, 3 };
+
+            assertClosestDivisors(divisors, divisors, cpi);
+        }
+
+        [Test]
+        public void TestExactDivisorsHighBPMStream()
+        {
+            var cpi = new ControlPointInfo();
+            cpi.Add(-50, new TimingControlPoint { BeatLength = 50 }); // 1200 BPM 1/4 (limit testing)
+
+            // A 1/4 stream should land on 1/1, 1/2 and 1/4 divisors.
+            double[] divisors = { 4, 4, 4, 4, 4, 4, 4, 4 };
+            double[] closestDivisors = { 4, 2, 4, 1, 4, 2, 4, 1 };
+
+            assertClosestDivisors(divisors, closestDivisors, cpi, step: 1 / 4d);
+        }
+
+        [Test]
+        public void TestApproximateDivisors()
+        {
+            var cpi = new ControlPointInfo();
+            cpi.Add(-1000, new TimingControlPoint { BeatLength = 1000 });
+
+            double[] divisors = { 3.03d, 0.97d, 14, 13, 7.94d, 6.08d, 3.93d, 2.96d, 2.02d, 64 };
+            double[] closestDivisors = { 3, 1, 16, 12, 8, 6, 4, 3, 2, 1 };
+
+            assertClosestDivisors(divisors, closestDivisors, cpi);
+        }
+
+        private void assertClosestDivisors(IReadOnlyList<double> divisors, IReadOnlyList<double> closestDivisors, ControlPointInfo cpi, double step = 1)
+        {
+            List<HitObject> hitobjects = new List<HitObject>();
+            double offset = cpi.TimingPoints[0].Time;
+
+            for (int i = 0; i < divisors.Count; ++i)
+            {
+                double beatLength = cpi.TimingPointAt(offset).BeatLength;
+                hitobjects.Add(new HitObject { StartTime = offset + beatLength / divisors[i] });
+                offset += beatLength * step;
+            }
+
+            var beatmap = new Beatmap
+            {
+                HitObjects = hitobjects,
+                ControlPointInfo = cpi
+            };
+
+            for (int i = 0; i < divisors.Count; ++i)
+                Assert.AreEqual(closestDivisors[i], beatmap.ClosestBeatDivisor(beatmap.HitObjects[i].StartTime), $"at index {i}");
+        }
+    }
+}