Merge branch 'develop' into stable

1 files changed, 520 insertions, 0 deletions

diff --git a/src/StardewModdingAPI.Tests/Core/ModResolverTests.cs b/src/StardewModdingAPI.Tests/Core/ModResolverTests.cs
new file mode 100644
index 00000000..b451465e
--- /dev/null
+++ b/src/StardewModdingAPI.Tests/Core/ModResolverTests.cs
@@ -0,0 +1,520 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using Moq;
+using Newtonsoft.Json;
+using NUnit.Framework;
+using StardewModdingAPI.Framework;
+using StardewModdingAPI.Framework.Models;
+using StardewModdingAPI.Framework.ModLoading;
+using StardewModdingAPI.Framework.Serialisation;
+
+namespace StardewModdingAPI.Tests.Core
+{
+    /// <summary>Unit tests for <see cref="ModResolver"/>.</summary>
+    [TestFixture]
+    public class ModResolverTests
+    {
+        /*********
+        ** Unit tests
+        *********/
+        /****
+        ** ReadManifests
+        ****/
+        [Test(Description = "Assert that the resolver correctly returns an empty list if there are no mods installed.")]
+        public void ReadBasicManifest_NoMods_ReturnsEmptyList()
+        {
+            // arrange
+            string rootFolder = Path.Combine(Path.GetTempPath(), Guid.NewGuid().ToString("N"));
+            Directory.CreateDirectory(rootFolder);
+
+            // act
+            IModMetadata[] mods = new ModResolver().ReadManifests(rootFolder, new JsonHelper(), new ModCompatibility[0], new DisabledMod[0]).ToArray();
+
+            // assert
+            Assert.AreEqual(0, mods.Length, 0, $"Expected to find zero manifests, found {mods.Length} instead.");
+        }
+
+        [Test(Description = "Assert that the resolver correctly returns a failed metadata if there's an empty mod folder.")]
+        public void ReadBasicManifest_EmptyModFolder_ReturnsFailedManifest()
+        {
+            // arrange
+            string rootFolder = Path.Combine(Path.GetTempPath(), Guid.NewGuid().ToString("N"));
+            string modFolder = Path.Combine(rootFolder, Guid.NewGuid().ToString("N"));
+            Directory.CreateDirectory(modFolder);
+
+            // act
+            IModMetadata[] mods = new ModResolver().ReadManifests(rootFolder, new JsonHelper(), new ModCompatibility[0], new DisabledMod[0]).ToArray();
+            IModMetadata mod = mods.FirstOrDefault();
+
+            // assert
+            Assert.AreEqual(1, mods.Length, 0, $"Expected to find one manifest, found {mods.Length} instead.");
+            Assert.AreEqual(ModMetadataStatus.Failed, mod.Status, "The mod metadata was not marked failed.");
+            Assert.IsNotNull(mod.Error, "The mod metadata did not have an error message set.");
+        }
+
+        [Test(Description = "Assert that the resolver correctly reads manifest data from a randomised file.")]
+        public void ReadBasicManifest_CanReadFile()
+        {
+            // create manifest data
+            IDictionary<string, object> originalDependency = new Dictionary<string, object>
+            {
+                [nameof(IManifestDependency.UniqueID)] = Sample.String()
+            };
+            IDictionary<string, object> original = new Dictionary<string, object>
+            {
+                [nameof(IManifest.Name)] = Sample.String(),
+                [nameof(IManifest.Author)] = Sample.String(),
+                [nameof(IManifest.Version)] = new SemanticVersion(Sample.Int(), Sample.Int(), Sample.Int(), Sample.String()),
+                [nameof(IManifest.Description)] = Sample.String(),
+                [nameof(IManifest.UniqueID)] = $"{Sample.String()}.{Sample.String()}",
+                [nameof(IManifest.EntryDll)] = $"{Sample.String()}.dll",
+                [nameof(IManifest.MinimumApiVersion)] = $"{Sample.Int()}.{Sample.Int()}-{Sample.String()}",
+                [nameof(IManifest.Dependencies)] = new[] { originalDependency },
+                ["ExtraString"] = Sample.String(),
+                ["ExtraInt"] = Sample.Int()
+            };
+
+            // write to filesystem
+            string rootFolder = Path.Combine(Path.GetTempPath(), Guid.NewGuid().ToString("N"));
+            string modFolder = Path.Combine(rootFolder, Guid.NewGuid().ToString("N"));
+            string filename = Path.Combine(modFolder, "manifest.json");
+            Directory.CreateDirectory(modFolder);
+            File.WriteAllText(filename, JsonConvert.SerializeObject(original));
+
+            // act
+            IModMetadata[] mods = new ModResolver().ReadManifests(rootFolder, new JsonHelper(), new ModCompatibility[0], new DisabledMod[0]).ToArray();
+            IModMetadata mod = mods.FirstOrDefault();
+
+            // assert
+            Assert.AreEqual(1, mods.Length, 0, "Expected to find one manifest.");
+            Assert.IsNotNull(mod, "The loaded manifest shouldn't be null.");
+            Assert.AreEqual(null, mod.Compatibility, "The compatibility record should be null since we didn't provide one.");
+            Assert.AreEqual(modFolder, mod.DirectoryPath, "The directory path doesn't match.");
+            Assert.AreEqual(ModMetadataStatus.Found, mod.Status, "The status doesn't match.");
+            Assert.AreEqual(null, mod.Error, "The error should be null since parsing should have succeeded.");
+
+            Assert.AreEqual(original[nameof(IManifest.Name)], mod.DisplayName, "The display name should use the manifest name.");
+            Assert.AreEqual(original[nameof(IManifest.Name)], mod.Manifest.Name, "The manifest's name doesn't match.");
+            Assert.AreEqual(original[nameof(IManifest.Author)], mod.Manifest.Author, "The manifest's author doesn't match.");
+            Assert.AreEqual(original[nameof(IManifest.Description)], mod.Manifest.Description, "The manifest's description doesn't match.");
+            Assert.AreEqual(original[nameof(IManifest.EntryDll)], mod.Manifest.EntryDll, "The manifest's entry DLL doesn't match.");
+            Assert.AreEqual(original[nameof(IManifest.MinimumApiVersion)], mod.Manifest.MinimumApiVersion?.ToString(), "The manifest's minimum API version doesn't match.");
+            Assert.AreEqual(original[nameof(IManifest.Version)]?.ToString(), mod.Manifest.Version?.ToString(), "The manifest's version doesn't match.");
+
+            Assert.IsNotNull(mod.Manifest.ExtraFields, "The extra fields should not be null.");
+            Assert.AreEqual(2, mod.Manifest.ExtraFields.Count, "The extra fields should contain two values.");
+            Assert.AreEqual(original["ExtraString"], mod.Manifest.ExtraFields["ExtraString"], "The manifest's extra fields should contain an 'ExtraString' value.");
+            Assert.AreEqual(original["ExtraInt"], mod.Manifest.ExtraFields["ExtraInt"], "The manifest's extra fields should contain an 'ExtraInt' value.");
+
+            Assert.IsNotNull(mod.Manifest.Dependencies, "The dependencies field should not be null.");
+            Assert.AreEqual(1, mod.Manifest.Dependencies.Length, "The dependencies field should contain one value.");
+            Assert.AreEqual(originalDependency[nameof(IManifestDependency.UniqueID)], mod.Manifest.Dependencies[0].UniqueID, "The first dependency's unique ID doesn't match.");
+        }
+
+        /****
+        ** ValidateManifests
+        ****/
+        [Test(Description = "Assert that validation doesn't fail if there are no mods installed.")]
+        public void ValidateManifests_NoMods_DoesNothing()
+        {
+            new ModResolver().ValidateManifests(new ModMetadata[0], apiVersion: new SemanticVersion("1.0"));
+        }
+
+        [Test(Description = "Assert that validation skips manifests that have already failed without calling any other properties.")]
+        public void ValidateManifests_Skips_Failed()
+        {
+            // arrange
+            Mock<IModMetadata> mock = new Mock<IModMetadata>(MockBehavior.Strict);
+            mock.Setup(p => p.Status).Returns(ModMetadataStatus.Failed);
+
+            // act
+            new ModResolver().ValidateManifests(new[] { mock.Object }, apiVersion: new SemanticVersion("1.0"));
+
+            // assert
+            mock.VerifyGet(p => p.Status, Times.Once, "The validation did not check the manifest status.");
+        }
+
+        [Test(Description = "Assert that validation fails if the mod has 'assume broken' compatibility.")]
+        public void ValidateManifests_ModCompatibility_AssumeBroken_Fails()
+        {
+            // arrange
+            Mock<IModMetadata> mock = new Mock<IModMetadata>(MockBehavior.Strict);
+            mock.Setup(p => p.Status).Returns(ModMetadataStatus.Found);
+            mock.Setup(p => p.Compatibility).Returns(new ModCompatibility { Compatibility = ModCompatibilityType.AssumeBroken });
+            mock.Setup(p => p.SetStatus(ModMetadataStatus.Failed, It.IsAny<string>())).Returns(() => mock.Object);
+
+            // act
+            new ModResolver().ValidateManifests(new[] { mock.Object }, apiVersion: new SemanticVersion("1.0"));
+
+            // assert
+            mock.Verify(p => p.SetStatus(ModMetadataStatus.Failed, It.IsAny<string>()), Times.Once, "The validation did not fail the metadata.");
+        }
+
+        [Test(Description = "Assert that validation fails when the minimum API version is higher than the current SMAPI version.")]
+        public void ValidateManifests_MinimumApiVersion_Fails()
+        {
+            // arrange
+            Mock<IModMetadata> mock = new Mock<IModMetadata>(MockBehavior.Strict);
+            mock.Setup(p => p.Status).Returns(ModMetadataStatus.Found);
+            mock.Setup(p => p.Compatibility).Returns(() => null);
+            mock.Setup(p => p.Manifest).Returns(this.GetManifest(m => m.MinimumApiVersion = new SemanticVersion("1.1")));
+            mock.Setup(p => p.SetStatus(ModMetadataStatus.Failed, It.IsAny<string>())).Returns(() => mock.Object);
+
+            // act
+            new ModResolver().ValidateManifests(new[] { mock.Object }, apiVersion: new SemanticVersion("1.0"));
+
+            // assert
+            mock.Verify(p => p.SetStatus(ModMetadataStatus.Failed, It.IsAny<string>()), Times.Once, "The validation did not fail the metadata.");
+        }
+
+        [Test(Description = "Assert that validation fails when the manifest references a DLL that does not exist.")]
+        public void ValidateManifests_MissingEntryDLL_Fails()
+        {
+            // arrange
+            Mock<IModMetadata> mock = new Mock<IModMetadata>(MockBehavior.Strict);
+            mock.Setup(p => p.Status).Returns(ModMetadataStatus.Found);
+            mock.Setup(p => p.Compatibility).Returns(() => null);
+            mock.Setup(p => p.Manifest).Returns(this.GetManifest());
+            mock.Setup(p => p.DirectoryPath).Returns(Path.GetTempPath());
+            mock.Setup(p => p.SetStatus(ModMetadataStatus.Failed, It.IsAny<string>())).Returns(() => mock.Object);
+
+            // act
+            new ModResolver().ValidateManifests(new[] { mock.Object }, apiVersion: new SemanticVersion("1.0"));
+
+            // assert
+            mock.Verify(p => p.SetStatus(ModMetadataStatus.Failed, It.IsAny<string>()), Times.Once, "The validation did not fail the metadata.");
+        }
+
+        [Test(Description = "Assert that validation fails when the manifest references a DLL that does not exist.")]
+        public void ValidateManifests_Valid_Passes()
+        {
+            // set up manifest
+            IManifest manifest = this.GetManifest();
+
+            // create DLL
+            string modFolder = Path.Combine(Path.GetTempPath(), Guid.NewGuid().ToString("N"));
+            Directory.CreateDirectory(modFolder);
+            File.WriteAllText(Path.Combine(modFolder, manifest.EntryDll), "");
+
+            // arrange
+            Mock<IModMetadata> mock = new Mock<IModMetadata>(MockBehavior.Strict);
+            mock.Setup(p => p.Status).Returns(ModMetadataStatus.Found);
+            mock.Setup(p => p.Compatibility).Returns(() => null);
+            mock.Setup(p => p.Manifest).Returns(manifest);
+            mock.Setup(p => p.DirectoryPath).Returns(modFolder);
+
+            // act
+            new ModResolver().ValidateManifests(new[] { mock.Object }, apiVersion: new SemanticVersion("1.0"));
+
+            // assert
+            // if Moq doesn't throw a method-not-setup exception, the validation didn't override the status.
+        }
+
+        /****
+        ** ProcessDependencies
+        ****/
+        [Test(Description = "Assert that processing dependencies doesn't fail if there are no mods installed.")]
+        public void ProcessDependencies_NoMods_DoesNothing()
+        {
+            // act
+            IModMetadata[] mods = new ModResolver().ProcessDependencies(new IModMetadata[0]).ToArray();
+
+            // assert
+            Assert.AreEqual(0, mods.Length, 0, "Expected to get an empty list of mods.");
+        }
+
+        [Test(Description = "Assert that processing dependencies doesn't change the order if there are no mod dependencies.")]
+        public void ProcessDependencies_NoDependencies_DoesNothing()
+        {
+            // arrange
+            // A B C
+            Mock<IModMetadata> modA = this.GetMetadata("Mod A");
+            Mock<IModMetadata> modB = this.GetMetadata("Mod B");
+            Mock<IModMetadata> modC = this.GetMetadata("Mod C");
+
+            // act
+            IModMetadata[] mods = new ModResolver().ProcessDependencies(new[] { modA.Object, modB.Object, modC.Object }).ToArray();
+
+            // assert
+            Assert.AreEqual(3, mods.Length, 0, "Expected to get the same number of mods input.");
+            Assert.AreSame(modA.Object, mods[0], "The load order unexpectedly changed with no dependencies.");
+            Assert.AreSame(modB.Object, mods[1], "The load order unexpectedly changed with no dependencies.");
+            Assert.AreSame(modC.Object, mods[2], "The load order unexpectedly changed with no dependencies.");
+        }
+
+        [Test(Description = "Assert that processing dependencies skips mods that have already failed without calling any other properties.")]
+        public void ProcessDependencies_Skips_Failed()
+        {
+            // arrange
+            Mock<IModMetadata> mock = new Mock<IModMetadata>(MockBehavior.Strict);
+            mock.Setup(p => p.Status).Returns(ModMetadataStatus.Failed);
+
+            // act
+            new ModResolver().ProcessDependencies(new[] { mock.Object });
+
+            // assert
+            mock.VerifyGet(p => p.Status, Times.Once, "The validation did not check the manifest status.");
+        }
+
+        [Test(Description = "Assert that simple dependencies are reordered correctly.")]
+        public void ProcessDependencies_Reorders_SimpleDependencies()
+        {
+            // arrange
+            // A ◀── B
+            // ▲     ▲
+            // │     │
+            // └─ C ─┘
+            Mock<IModMetadata> modA = this.GetMetadata("Mod A");
+            Mock<IModMetadata> modB = this.GetMetadata("Mod B", dependencies: new[] { "Mod A" });
+            Mock<IModMetadata> modC = this.GetMetadata("Mod C", dependencies: new[] { "Mod A", "Mod B" });
+
+            // act
+            IModMetadata[] mods = new ModResolver().ProcessDependencies(new[] { modC.Object, modA.Object, modB.Object }).ToArray();
+
+            // assert
+            Assert.AreEqual(3, mods.Length, 0, "Expected to get the same number of mods input.");
+            Assert.AreSame(modA.Object, mods[0], "The load order is incorrect: mod A should be first since the other mods depend on it.");
+            Assert.AreSame(modB.Object, mods[1], "The load order is incorrect: mod B should be second since it needs mod A, and is needed by mod C.");
+            Assert.AreSame(modC.Object, mods[2], "The load order is incorrect: mod C should be third since it needs both mod A and mod B.");
+        }
+
+        [Test(Description = "Assert that simple dependency chains are reordered correctly.")]
+        public void ProcessDependencies_Reorders_DependencyChain()
+        {
+            // arrange
+            // A ◀── B ◀── C ◀── D
+            Mock<IModMetadata> modA = this.GetMetadata("Mod A");
+            Mock<IModMetadata> modB = this.GetMetadata("Mod B", dependencies: new[] { "Mod A" });
+            Mock<IModMetadata> modC = this.GetMetadata("Mod C", dependencies: new[] { "Mod B" });
+            Mock<IModMetadata> modD = this.GetMetadata("Mod D", dependencies: new[] { "Mod C" });
+
+            // act
+            IModMetadata[] mods = new ModResolver().ProcessDependencies(new[] { modC.Object, modA.Object, modB.Object, modD.Object }).ToArray();
+
+            // assert
+            Assert.AreEqual(4, mods.Length, 0, "Expected to get the same number of mods input.");
+            Assert.AreSame(modA.Object, mods[0], "The load order is incorrect: mod A should be first since it's needed by mod B.");
+            Assert.AreSame(modB.Object, mods[1], "The load order is incorrect: mod B should be second since it needs mod A, and is needed by mod C.");
+            Assert.AreSame(modC.Object, mods[2], "The load order is incorrect: mod C should be third since it needs mod B, and is needed by mod D.");
+            Assert.AreSame(modD.Object, mods[3], "The load order is incorrect: mod D should be fourth since it needs mod C.");
+        }
+
+        [Test(Description = "Assert that overlapping dependency chains are reordered correctly.")]
+        public void ProcessDependencies_Reorders_OverlappingDependencyChain()
+        {
+            // arrange
+            // A ◀── B ◀── C ◀── D
+            //       ▲     ▲
+            //       │     │
+            //       E ◀── F
+            Mock<IModMetadata> modA = this.GetMetadata("Mod A");
+            Mock<IModMetadata> modB = this.GetMetadata("Mod B", dependencies: new[] { "Mod A" });
+            Mock<IModMetadata> modC = this.GetMetadata("Mod C", dependencies: new[] { "Mod B" });
+            Mock<IModMetadata> modD = this.GetMetadata("Mod D", dependencies: new[] { "Mod C" });
+            Mock<IModMetadata> modE = this.GetMetadata("Mod E", dependencies: new[] { "Mod B" });
+            Mock<IModMetadata> modF = this.GetMetadata("Mod F", dependencies: new[] { "Mod C", "Mod E" });
+
+            // act
+            IModMetadata[] mods = new ModResolver().ProcessDependencies(new[] { modC.Object, modA.Object, modB.Object, modD.Object, modF.Object, modE.Object }).ToArray();
+
+            // assert
+            Assert.AreEqual(6, mods.Length, 0, "Expected to get the same number of mods input.");
+            Assert.AreSame(modA.Object, mods[0], "The load order is incorrect: mod A should be first since it's needed by mod B.");
+            Assert.AreSame(modB.Object, mods[1], "The load order is incorrect: mod B should be second since it needs mod A, and is needed by mod C.");
+            Assert.AreSame(modC.Object, mods[2], "The load order is incorrect: mod C should be third since it needs mod B, and is needed by mod D.");
+            Assert.AreSame(modD.Object, mods[3], "The load order is incorrect: mod D should be fourth since it needs mod C.");
+            Assert.AreSame(modE.Object, mods[4], "The load order is incorrect: mod E should be fifth since it needs mod B, but is specified after C which also needs mod B.");
+            Assert.AreSame(modF.Object, mods[5], "The load order is incorrect: mod F should be last since it needs mods E and C.");
+        }
+
+        [Test(Description = "Assert that mods with circular dependency chains are skipped, but any other mods are loaded in the correct order.")]
+        public void ProcessDependencies_Skips_CircularDependentMods()
+        {
+            // arrange
+            // A ◀── B ◀── C ──▶ D
+            //             ▲     │
+            //             │     ▼
+            //             └──── E
+            Mock<IModMetadata> modA = this.GetMetadata("Mod A");
+            Mock<IModMetadata> modB = this.GetMetadata("Mod B", dependencies: new[] { "Mod A" });
+            Mock<IModMetadata> modC = this.GetMetadata("Mod C", dependencies: new[] { "Mod B", "Mod D" }, allowStatusChange: true);
+            Mock<IModMetadata> modD = this.GetMetadata("Mod D", dependencies: new[] { "Mod E" }, allowStatusChange: true);
+            Mock<IModMetadata> modE = this.GetMetadata("Mod E", dependencies: new[] { "Mod C" }, allowStatusChange: true);
+
+            // act
+            IModMetadata[] mods = new ModResolver().ProcessDependencies(new[] { modC.Object, modA.Object, modB.Object, modD.Object, modE.Object }).ToArray();
+
+            // assert
+            Assert.AreEqual(5, mods.Length, 0, "Expected to get the same number of mods input.");
+            Assert.AreSame(modA.Object, mods[0], "The load order is incorrect: mod A should be first since it's needed by mod B.");
+            Assert.AreSame(modB.Object, mods[1], "The load order is incorrect: mod B should be second since it needs mod A.");
+            modC.Verify(p => p.SetStatus(ModMetadataStatus.Failed, It.IsAny<string>()), Times.Once, "Mod C was expected to fail since it's part of a dependency loop.");
+            modD.Verify(p => p.SetStatus(ModMetadataStatus.Failed, It.IsAny<string>()), Times.Once, "Mod D was expected to fail since it's part of a dependency loop.");
+            modE.Verify(p => p.SetStatus(ModMetadataStatus.Failed, It.IsAny<string>()), Times.Once, "Mod E was expected to fail since it's part of a dependency loop.");
+        }
+
+        [Test(Description = "Assert that dependencies are sorted correctly even if some of the mods failed during metadata loading.")]
+        public void ProcessDependencies_WithSomeFailedMods_Succeeds()
+        {
+            // arrange
+            // A ◀── B ◀── C   D (failed)
+            Mock<IModMetadata> modA = this.GetMetadata("Mod A");
+            Mock<IModMetadata> modB = this.GetMetadata("Mod B", dependencies: new[] { "Mod A" });
+            Mock<IModMetadata> modC = this.GetMetadata("Mod C", dependencies: new[] { "Mod B" }, allowStatusChange: true);
+            Mock<IModMetadata> modD = new Mock<IModMetadata>(MockBehavior.Strict);
+            modD.Setup(p => p.Manifest).Returns<IManifest>(null);
+            modD.Setup(p => p.Status).Returns(ModMetadataStatus.Failed);
+
+            // act
+            IModMetadata[] mods = new ModResolver().ProcessDependencies(new[] { modC.Object, modA.Object, modB.Object, modD.Object }).ToArray();
+
+            // assert
+            Assert.AreEqual(4, mods.Length, 0, "Expected to get the same number of mods input.");
+            Assert.AreSame(modD.Object, mods[0], "The load order is incorrect: mod D should be first since it was already failed.");
+            Assert.AreSame(modA.Object, mods[1], "The load order is incorrect: mod A should be second since it's needed by mod B.");
+            Assert.AreSame(modB.Object, mods[2], "The load order is incorrect: mod B should be third since it needs mod A, and is needed by mod C.");
+            Assert.AreSame(modC.Object, mods[3], "The load order is incorrect: mod C should be fourth since it needs mod B, and is needed by mod D.");
+        }
+
+        [Test(Description = "Assert that dependencies are failed if they don't meet the minimum version.")]
+        public void ProcessDependencies_WithMinVersions_FailsIfNotMet()
+        {
+            // arrange
+            // A 1.0 ◀── B (need A 1.1)
+            Mock<IModMetadata> modA = this.GetMetadata(this.GetManifest("Mod A", "1.0"));
+            Mock<IModMetadata> modB = this.GetMetadata(this.GetManifest("Mod B", "1.0", new ManifestDependency("Mod A", "1.1")), allowStatusChange: true);
+
+            // act
+            IModMetadata[] mods = new ModResolver().ProcessDependencies(new[] { modA.Object, modB.Object }).ToArray();
+
+            // assert
+            Assert.AreEqual(2, mods.Length, 0, "Expected to get the same number of mods input.");
+            modB.Verify(p => p.SetStatus(ModMetadataStatus.Failed, It.IsAny<string>()), Times.Once, "Mod B unexpectedly didn't fail even though it needs a newer version of Mod A.");
+        }
+
+        [Test(Description = "Assert that dependencies are accepted if they meet the minimum version.")]
+        public void ProcessDependencies_WithMinVersions_SucceedsIfMet()
+        {
+            // arrange
+            // A 1.0 ◀── B (need A 1.0-beta)
+            Mock<IModMetadata> modA = this.GetMetadata(this.GetManifest("Mod A", "1.0"));
+            Mock<IModMetadata> modB = this.GetMetadata(this.GetManifest("Mod B", "1.0", new ManifestDependency("Mod A", "1.0-beta")), allowStatusChange: false);
+
+            // act
+            IModMetadata[] mods = new ModResolver().ProcessDependencies(new[] { modA.Object, modB.Object }).ToArray();
+
+            // assert
+            Assert.AreEqual(2, mods.Length, 0, "Expected to get the same number of mods input.");
+            Assert.AreSame(modA.Object, mods[0], "The load order is incorrect: mod A should be first since it's needed by mod B.");
+            Assert.AreSame(modB.Object, mods[1], "The load order is incorrect: mod B should be second since it needs mod A.");
+        }
+
+#if SMAPI_2_0
+        [Test(Description = "Assert that optional dependencies are sorted correctly if present.")]
+        public void ProcessDependencies_IfOptional()
+        {
+            // arrange
+            // A ◀── B
+            Mock<IModMetadata> modA = this.GetMetadata(this.GetManifest("Mod A", "1.0"));
+            Mock<IModMetadata> modB = this.GetMetadata(this.GetManifest("Mod B", "1.0", new ManifestDependency("Mod A", "1.0", required: false)), allowStatusChange: false);
+
+            // act
+            IModMetadata[] mods = new ModResolver().ProcessDependencies(new[] { modB.Object, modA.Object }).ToArray();
+
+            // assert
+            Assert.AreEqual(2, mods.Length, 0, "Expected to get the same number of mods input.");
+            Assert.AreSame(modA.Object, mods[0], "The load order is incorrect: mod A should be first since it's needed by mod B.");
+            Assert.AreSame(modB.Object, mods[1], "The load order is incorrect: mod B should be second since it needs mod A.");
+        }
+
+        [Test(Description = "Assert that optional dependencies are accepted if they're missing.")]
+        public void ProcessDependencies_IfOptional_SucceedsIfMissing()
+        {
+            // arrange
+            // A ◀── B where A doesn't exist
+            Mock<IModMetadata> modB = this.GetMetadata(this.GetManifest("Mod B", "1.0", new ManifestDependency("Mod A", "1.0", required: false)), allowStatusChange: false);
+
+            // act
+            IModMetadata[] mods = new ModResolver().ProcessDependencies(new[] { modB.Object }).ToArray();
+
+            // assert
+            Assert.AreEqual(1, mods.Length, 0, "Expected to get the same number of mods input.");
+            Assert.AreSame(modB.Object, mods[0], "The load order is incorrect: mod B should be first since it's the only mod.");
+        }
+#endif
+
+
+        /*********
+        ** Private methods
+        *********/
+        /// <summary>Get a randomised basic manifest.</summary>
+        /// <param name="adjust">Adjust the generated manifest.</param>
+        private Manifest GetManifest(Action<Manifest> adjust = null)
+        {
+            Manifest manifest = new Manifest
+            {
+                Name = Sample.String(),
+                Author = Sample.String(),
+                Version = new SemanticVersion(Sample.Int(), Sample.Int(), Sample.Int(), Sample.String()),
+                Description = Sample.String(),
+                UniqueID = $"{Sample.String()}.{Sample.String()}",
+                EntryDll = $"{Sample.String()}.dll"
+            };
+            adjust?.Invoke(manifest);
+            return manifest;
+        }
+
+        /// <summary>Get a randomised basic manifest.</summary>
+        /// <param name="uniqueID">The mod's name and unique ID.</param>
+        /// <param name="version">The mod version.</param>
+        /// <param name="dependencies">The dependencies this mod requires.</param>
+        private IManifest GetManifest(string uniqueID, string version, params IManifestDependency[] dependencies)
+        {
+            return this.GetManifest(manifest =>
+            {
+                manifest.Name = uniqueID;
+                manifest.UniqueID = uniqueID;
+                manifest.Version = new SemanticVersion(version);
+                manifest.Dependencies = dependencies;
+            });
+        }
+
+        /// <summary>Get a randomised basic manifest.</summary>
+        /// <param name="uniqueID">The mod's name and unique ID.</param>
+        private Mock<IModMetadata> GetMetadata(string uniqueID)
+        {
+            return this.GetMetadata(this.GetManifest(uniqueID, "1.0"));
+        }
+
+        /// <summary>Get a randomised basic manifest.</summary>
+        /// <param name="uniqueID">The mod's name and unique ID.</param>
+        /// <param name="dependencies">The dependencies this mod requires.</param>
+        /// <param name="allowStatusChange">Whether the code being tested is allowed to change the mod status.</param>
+        private Mock<IModMetadata> GetMetadata(string uniqueID, string[] dependencies, bool allowStatusChange = false)
+        {
+            IManifest manifest = this.GetManifest(uniqueID, "1.0", dependencies?.Select(dependencyID => (IManifestDependency)new ManifestDependency(dependencyID, null)).ToArray());
+            return this.GetMetadata(manifest, allowStatusChange);
+        }
+
+        /// <summary>Get a randomised basic manifest.</summary>
+        /// <param name="manifest">The mod manifest.</param>
+        /// <param name="allowStatusChange">Whether the code being tested is allowed to change the mod status.</param>
+        private Mock<IModMetadata> GetMetadata(IManifest manifest, bool allowStatusChange = false)
+        {
+            Mock<IModMetadata> mod = new Mock<IModMetadata>(MockBehavior.Strict);
+            mod.Setup(p => p.Status).Returns(ModMetadataStatus.Found);
+            mod.Setup(p => p.DisplayName).Returns(manifest.UniqueID);
+            mod.Setup(p => p.Manifest).Returns(manifest);
+            if (allowStatusChange)
+            {
+                mod
+                    .Setup(p => p.SetStatus(It.IsAny<ModMetadataStatus>(), It.IsAny<string>()))
+                    .Callback<ModMetadataStatus, string>((status, message) => Console.WriteLine($"<{manifest.UniqueID} changed status: [{status}] {message}"))
+                    .Returns(mod.Object);
+            }
+            return mod;
+        }
+    }
+}