fix: Add unit test suite

tests/ActorSrcGen.Tests/GeneratorTests.cs

@@ -0,0 +1,47 @@
+using System.Linq;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Xunit;
+
+namespace ActorSrcGen.Tests;
+
+public class GeneratorTests
+{
+    [Fact]
+    public void Generator_Executes_Without_Errors()
+    {
+        var source = """
+            using ActorSrcGen;
+
+            [Actor]
+            public class TestActor
+            {
+                [Step]
+                public void Initialize() { }
+            }
+            """;
+
+        var compilation = CreateCompilation(source);
+        var generator = new ActorGenerator();
+        var driver = CSharpGeneratorDriver.Create(generator);
+
+        var runResult = driver.RunGenerators(compilation).GetRunResult();
+        var diagnostics = runResult.Diagnostics
+            .Where(d => d.Severity == DiagnosticSeverity.Error)
+            .ToList();
+
+        Assert.Empty(diagnostics);
+    }
+
+    private static CSharpCompilation CreateCompilation(string source) =>
+        CSharpCompilation.Create(
+            "TestAssembly",
+            new[] { CSharpSyntaxTree.ParseText(source) },
+            references: new[]
+            {
+                MetadataReference.CreateFromFile(typeof(object).Assembly.Location),
+                MetadataReference.CreateFromFile(typeof(Console).Assembly.Location),
+                MetadataReference.CreateFromFile(typeof(ActorSrcGen.IActor<>).Assembly.Location)
+            },
+            options: new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary));
+}