Update SA1206 for readonly members

Author: sharwell

StyleCop.Analyzers/StyleCop.Analyzers.Test.CSharp8/OrderingRules/SA1206CodeFixProviderCSharp8UnitTests.cs

@@ -3,9 +3,112 @@
 
 namespace StyleCop.Analyzers.Test.CSharp8.OrderingRules
 {
+    using System.Threading;
+    using System.Threading.Tasks;
+    using Microsoft.CodeAnalysis.Testing;
     using StyleCop.Analyzers.Test.CSharp7.OrderingRules;
+    using Xunit;
+    using static StyleCop.Analyzers.Test.Verifiers.StyleCopCodeFixVerifier<
+        StyleCop.Analyzers.OrderingRules.SA1206DeclarationKeywordsMustFollowOrder,
+        StyleCop.Analyzers.OrderingRules.SA1206CodeFixProvider>;
 
     public partial class SA1206CodeFixProviderCSharp8UnitTests : SA1206CodeFixProviderCSharp7UnitTests
     {
+        [Fact]
+        [WorkItem(3001, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3001")]
+        public async Task VerifyReadonlyKeywordReorderingInStructMethodAsync()
+        {
+            var testCode = @"
+public struct S
+{
+    readonly {|#0:public|} void M()
+    {
+    }
+}";
+
+            var fixedCode = @"
+public struct S
+{
+    public readonly void M()
+    {
+    }
+}";
+
+            var expected = Diagnostic().WithLocation(0).WithArguments("public", "readonly");
+            await VerifyCSharpFixAsync(testCode, expected, fixedCode, CancellationToken.None).ConfigureAwait(false);
+        }
+
+        [Fact]
+        [WorkItem(3001, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3001")]
+        public async Task VerifyReadonlyKeywordReorderingInStructPropertyAsync()
+        {
+            var testCode = @"
+public struct S
+{
+    readonly {|#0:internal|} int Value { get; }
+}";
+
+            var fixedCode = @"
+public struct S
+{
+    internal readonly int Value { get; }
+}";
+
+            var expected = Diagnostic().WithLocation(0).WithArguments("internal", "readonly");
+            await VerifyCSharpFixAsync(testCode, expected, fixedCode, CancellationToken.None).ConfigureAwait(false);
+        }
+
+        [Fact]
+        [WorkItem(3001, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3001")]
+        public async Task VerifyReadonlyKeywordReorderingWithOtherModifiersAsync()
+        {
+            var testCode = @"
+public struct S
+{
+    readonly override {|#0:public|} string ToString() => string.Empty;
+}";
+
+            var fixedCode = @"
+public struct S
+{
+    public readonly override string ToString() => string.Empty;
+}";
+
+            var expected = Diagnostic().WithLocation(0).WithArguments("public", "override");
+            await VerifyCSharpFixAsync(testCode, expected, fixedCode, CancellationToken.None).ConfigureAwait(false);
+        }
+
+        [Fact]
+        [WorkItem(3001, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3001")]
+        public async Task VerifyReadonlyKeywordReorderingWithAccessAndStaticAsync()
+        {
+            var testCode = @"
+public struct S
+{
+    readonly {|#0:static|} {|#1:public|} int {|#2:M|}() => 0;
+}";
+
+            var fixedCode = @"
+public struct S
+{
+    public static readonly int {|#2:M|}() => 0;
+}";
+
+            var test = new CSharpTest
+            {
+                TestCode = testCode,
+                FixedCode = fixedCode,
+                ExpectedDiagnostics =
+                {
+                    Diagnostic().WithLocation(0).WithArguments("static", "readonly"),
+                    Diagnostic().WithLocation(1).WithArguments("public", "readonly"),
+
+                    // /0/Test0.cs(4,32): error CS8657: Static member 'S.M()' cannot be marked 'readonly'.
+                    DiagnosticResult.CompilerError("CS8657").WithLocation(2).WithArguments("S.M()"),
+                },
+            };
+
+            await test.RunAsync(CancellationToken.None).ConfigureAwait(false);
+        }
     }
 }