Add unit test for code fixer

Author: Sergio0694

tests/CommunityToolkit.Mvvm.SourceGenerators.Roslyn4120.UnitTests/Test_UseObservablePropertyOnSemiAutoPropertyCodeFixer.cs

@@ -0,0 +1,76 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Threading.Tasks;
+using CommunityToolkit.Mvvm.ComponentModel;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.Testing;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using CSharpCodeFixTest = CommunityToolkit.Mvvm.SourceGenerators.UnitTests.Helpers.CSharpCodeFixWithLanguageVersionTest<
+    CommunityToolkit.Mvvm.SourceGenerators.UseObservablePropertyOnSemiAutoPropertyAnalyzer,
+    CommunityToolkit.Mvvm.CodeFixers.UsePartialPropertyForSemiAutoPropertyCodeFixer,
+    Microsoft.CodeAnalysis.Testing.DefaultVerifier>;
+using CSharpCodeFixVerifier = Microsoft.CodeAnalysis.CSharp.Testing.CSharpCodeFixVerifier<
+    CommunityToolkit.Mvvm.SourceGenerators.UseObservablePropertyOnSemiAutoPropertyAnalyzer,
+    CommunityToolkit.Mvvm.CodeFixers.UsePartialPropertyForSemiAutoPropertyCodeFixer,
+    Microsoft.CodeAnalysis.Testing.DefaultVerifier>;
+
+namespace CommunityToolkit.Mvvm.SourceGenerators.UnitTests;
+
+[TestClass]
+public class Test_UseObservablePropertyOnSemiAutoPropertyCodeFixer
+{
+    [TestMethod]
+    public async Task SimpleProperty()
+    {
+        string original = """
+            using CommunityToolkit.Mvvm.ComponentModel;
+
+            namespace MyApp;
+
+            public class SampleViewModel : ObservableObject
+            {
+                public string Name
+                {
+                    get => field;
+                    set => SetProperty(ref field, value);
+                }
+            }
+            """;
+
+        string @fixed = """
+            using CommunityToolkit.Mvvm.ComponentModel;
+
+            namespace MyApp;
+
+            public partial class SampleViewModel : ObservableObject
+            {
+                [ObservableProperty]
+                public partial string Name { get; set; }
+            }
+            """;
+
+        CSharpCodeFixTest test = new(LanguageVersion.Preview)
+        {
+            TestCode = original,
+            FixedCode = @fixed,
+            ReferenceAssemblies = ReferenceAssemblies.Net.Net80,
+        };
+
+        test.TestState.AdditionalReferences.Add(typeof(ObservableObject).Assembly);
+        test.ExpectedDiagnostics.AddRange(new[]
+        {
+            // /0/Test0.cs(7,19): info MVVMTK0056: The semi-auto property MyApp.SampleViewModel.Name can be converted to a partial property using [ObservableProperty], which is recommended (doing so makes the code less verbose and results in more optimized code)
+            CSharpCodeFixVerifier.Diagnostic().WithSpan(7, 19, 7, 23).WithArguments("MyApp.SampleViewModel", "Name"),
+        });
+
+        test.FixedState.ExpectedDiagnostics.AddRange(new[]
+        {
+            // /0/Test0.cs(6,24): error CS9248: Partial property 'C.I' must have an implementation part.
+            DiagnosticResult.CompilerError("CS9248").WithSpan(6, 24, 6, 25).WithArguments("C.I"),
+        });
+
+        await test.RunAsync();
+    }
+}