diff --git a/osu.Game.Tests/Mods/ModDifficultyAdjustTest.cs b/osu.Game.Tests/Mods/ModDifficultyAdjustTest.cs
new file mode 100644
index 0000000000..fcbdcbe724
--- /dev/null
+++ b/osu.Game.Tests/Mods/ModDifficultyAdjustTest.cs
@@ -0,0 +1,168 @@
+// 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.Online.API;
+using osu.Game.Rulesets;
+using osu.Game.Rulesets.Difficulty;
+using osu.Game.Rulesets.Mods;
+using osu.Game.Rulesets.UI;
+
+namespace osu.Game.Tests.Mods
+{
+    [TestFixture]
+    [Ignore("Currently broken, pending fixes/reworking of ModDifficultyAdjust.")]
+    public class ModDifficultyAdjustTest
+    {
+        // Todo: This shouldn't exist, but is currently required for the mod to accept a new BeatmapDifficulty object...
+        private int currentId;
+
+        private TestModDifficultyAdjust testMod;
+
+        [SetUp]
+        public void Setup()
+        {
+            currentId = 0;
+            testMod = new TestModDifficultyAdjust();
+
+            // Todo: This shouldn't be a thing, but is currently required because this causes the mod to keep track of the bindables internally...
+            applyDifficulty(new BeatmapDifficulty
+            {
+                DrainRate = -1,
+                OverallDifficulty = -1
+            });
+        }
+
+        [Test]
+        public void TestUnchangedSettingsFollowAppliedDifficulty()
+        {
+            var result = applyDifficulty(new BeatmapDifficulty
+            {
+                DrainRate = 10,
+                OverallDifficulty = 10
+            });
+
+            Assert.That(result.DrainRate, Is.EqualTo(10));
+            Assert.That(result.OverallDifficulty, Is.EqualTo(10));
+
+            result = applyDifficulty(new BeatmapDifficulty
+            {
+                DrainRate = 1,
+                OverallDifficulty = 1
+            });
+
+            Assert.That(result.DrainRate, Is.EqualTo(1));
+            Assert.That(result.OverallDifficulty, Is.EqualTo(1));
+        }
+
+        [Test]
+        public void TestChangedSettingsOverrideAppliedDifficulty()
+        {
+            testMod.OverallDifficulty.Value = 4;
+
+            var result = applyDifficulty(new BeatmapDifficulty
+            {
+                DrainRate = 10,
+                OverallDifficulty = 10
+            });
+
+            Assert.That(result.DrainRate, Is.EqualTo(10));
+            Assert.That(result.OverallDifficulty, Is.EqualTo(4));
+
+            result = applyDifficulty(new BeatmapDifficulty
+            {
+                DrainRate = 1,
+                OverallDifficulty = 1
+            });
+
+            Assert.That(result.DrainRate, Is.EqualTo(1));
+            Assert.That(result.OverallDifficulty, Is.EqualTo(4));
+        }
+
+        [Test]
+        public void TestChangedSettingsRetainedWhenSameValueIsApplied()
+        {
+            testMod.OverallDifficulty.Value = 4;
+
+            // Apply and de-apply the same value as the mod.
+            applyDifficulty(new BeatmapDifficulty { OverallDifficulty = 4 });
+            var result = applyDifficulty(new BeatmapDifficulty { OverallDifficulty = 10 });
+
+            Assert.That(result.OverallDifficulty, Is.EqualTo(4));
+        }
+
+        [Test]
+        public void TestChangedSettingSerialisedWhenSameValueIsApplied()
+        {
+            applyDifficulty(new BeatmapDifficulty { OverallDifficulty = 4 });
+            testMod.OverallDifficulty.Value = 4;
+
+            var result = (TestModDifficultyAdjust)new APIMod(testMod).ToMod(new TestRuleset());
+
+            Assert.That(result.OverallDifficulty.Value, Is.EqualTo(4));
+        }
+
+        [Test]
+        public void TestChangedSettingsRevertedToDefault()
+        {
+            applyDifficulty(new BeatmapDifficulty
+            {
+                DrainRate = 10,
+                OverallDifficulty = 10
+            });
+
+            testMod.OverallDifficulty.Value = 4;
+            testMod.ResetSettingsToDefaults();
+
+            Assert.That(testMod.DrainRate.Value, Is.EqualTo(10));
+            Assert.That(testMod.OverallDifficulty.Value, Is.EqualTo(10));
+        }
+
+        /// <summary>
+        /// Applies a <see cref="BeatmapDifficulty"/> to the mod and returns a new <see cref="BeatmapDifficulty"/>
+        /// representing the result if the mod were applied to a fresh <see cref="BeatmapDifficulty"/> instance.
+        /// </summary>
+        private BeatmapDifficulty applyDifficulty(BeatmapDifficulty difficulty)
+        {
+            difficulty.ID = ++currentId;
+            testMod.ReadFromDifficulty(difficulty);
+
+            var newDifficulty = new BeatmapDifficulty();
+            testMod.ApplyToDifficulty(newDifficulty);
+            return newDifficulty;
+        }
+
+        private class TestModDifficultyAdjust : ModDifficultyAdjust
+        {
+        }
+
+        private class TestRuleset : Ruleset
+        {
+            public override IEnumerable<Mod> GetModsFor(ModType type)
+            {
+                if (type == ModType.DifficultyIncrease)
+                    yield return new TestModDifficultyAdjust();
+            }
+
+            public override DrawableRuleset CreateDrawableRulesetWith(IBeatmap beatmap, IReadOnlyList<Mod> mods = null)
+            {
+                throw new System.NotImplementedException();
+            }
+
+            public override IBeatmapConverter CreateBeatmapConverter(IBeatmap beatmap)
+            {
+                throw new System.NotImplementedException();
+            }
+
+            public override DifficultyCalculator CreateDifficultyCalculator(WorkingBeatmap beatmap)
+            {
+                throw new System.NotImplementedException();
+            }
+
+            public override string Description => string.Empty;
+            public override string ShortName => string.Empty;
+        }
+    }
+}