1 files changed, 118 insertions, 0 deletions
diff --git a/src/SMAPI.ModBuildConfig.Analyzer.Tests/UnitTests.cs b/src/SMAPI.ModBuildConfig.Analyzer.Tests/UnitTests.cs
new file mode 100644
index 00000000..d5e4ef52
--- /dev/null
+++ b/src/SMAPI.ModBuildConfig.Analyzer.Tests/UnitTests.cs
@@ -0,0 +1,118 @@
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Diagnostics;
+using NUnit.Framework;
+using SMAPI.ModBuildConfig.Analyzer.Tests.Framework;
+using StardewModdingAPI.ModBuildConfig.Analyzer;
+
+namespace SMAPI.ModBuildConfig.Analyzer.Tests
+{
+    /// <summary>Unit tests for the C# analyzers.</summary>
+    [TestFixture]
+    public class UnitTests : DiagnosticVerifier
+    {
+        /*********
+        ** Properties
+        *********/
+        /// <summary>Sample C# code which contains a simplified representation of Stardew Valley's <c>Netcode</c> types, and sample mod code with a {{test-code}} placeholder for the code being tested.</summary>
+        const string SampleProgram = @"
+            using System;
+            using Netcode;
+
+            namespace Netcode
+            {
+                public class NetInt : NetFieldBase<int, NetInt> { }
+                public class NetRef : NetFieldBase<object, NetRef> { }
+                public class NetFieldBase<T, TSelf> where TSelf : NetFieldBase<T, TSelf>
+                {
+                    public T Value { get; set; }
+                    public static implicit operator T(NetFieldBase<T, TSelf> field) => field.Value;
+                }
+            }
+
+            namespace SampleMod
+            {
+                class Item
+                {
+                    public NetInt category { get; } = new NetInt { Value = 42 };
+                }
+
+                class ModEntry
+                {
+                    public void Entry()
+                    {
+                        NetInt intField = new NetInt { Value = 42 };
+                        NetRef refField = new NetRef { Value = null };
+                        Item item = null;
+
+                        // this line should raise diagnostics
+                        {{test-code}} // line 32
+
+                        // these lines should not
+                        if ((int)field != 42);
+                    }
+                }
+            }
+        ";
+
+        /// <summary>The line number where the unit tested code is injected into <see cref="SampleProgram"/>.</summary>
+        private const int SampleCodeLine = 32;
+
+        /// <summary>The column number where the unit tested code is injected into <see cref="SampleProgram"/>.</summary>
+        private const int SampleCodeColumn = 25;
+
+
+        /*********
+        ** Unit tests
+        *********/
+        /// <summary>Test that no diagnostics are raised for an empty code block.</summary>
+        [TestCase]
+        public void EmptyCode_HasNoDiagnostics()
+        {
+            // arrange
+            string test = @"";
+
+            // assert
+            this.VerifyCSharpDiagnostic(test);
+        }
+
+        /// <summary>Test that the expected diagnostic message is raised.</summary>
+        /// <param name="codeText">The code line to test.</param>
+        /// <param name="column">The column within the code line where the diagnostic message should be reported.</param>
+        /// <param name="expression">The expression which should be reported.</param>
+        /// <param name="fromType">The source type name which should be reported.</param>
+        /// <param name="toType">The target type name which should be reported.</param>
+        [TestCase("if (intField < 42);", 4, "intField", "NetInt", "Int32")]
+        [TestCase("if (intField <= 42);", 4, "intField", "NetInt", "Int32")]
+        [TestCase("if (intField > 42);", 4, "intField", "NetInt", "Int32")]
+        [TestCase("if (intField >= 42);", 4, "intField", "NetInt", "Int32")]
+        [TestCase("if (intField == 42);", 4, "intField", "NetInt", "Int32")]
+        [TestCase("if (intField != 42);", 4, "intField", "NetInt", "Int32")]
+        [TestCase("if (refField != null);", 4, "refField", "NetRef", "Object")]
+        [TestCase("if (item?.category != 42);", 4, "item?.category", "NetInt", "Int32")]
+        public void ImplicitComparisons_RaiseDiagnostics(string codeText, int column, string expression, string fromType, string toType)
+        {
+            // arrange
+            string code = UnitTests.SampleProgram.Replace("{{test-code}}", codeText);
+            DiagnosticResult expected = new DiagnosticResult
+            {
+                Id = "SMAPI001",
+                Message = $"This implicitly converts '{expression}' from {fromType} to {toType}, but {fromType} has unintuitive implicit conversion rules. Consider comparing against the actual value instead to avoid bugs. See https://smapi.io/buildmsg/SMAPI001 for details.",
+                Severity = DiagnosticSeverity.Warning,
+                Locations = new[] { new DiagnosticResultLocation("Test0.cs", UnitTests.SampleCodeLine, UnitTests.SampleCodeColumn + column) }
+            };
+
+            // assert
+            this.VerifyCSharpDiagnostic(code, expected);
+        }
+
+
+        /*********
+        ** Helpers
+        *********/
+        /// <summary>Get the analyzer being tested.</summary>
+        protected override DiagnosticAnalyzer GetCSharpDiagnosticAnalyzer()
+        {
+            return new ImplicitNetFieldCastAnalyzer();
+        }
+    }
+}