Added documentation for test helpers

src/EditorFeatures/TestUtilities/CodeActions/CSharpCodeFixVerifier`2+Test.cs

@@ -19,6 +19,13 @@ public static partial class CSharpCodeFixVerifier<TAnalyzer, TCodeFix>
     {
         public class Test : CSharpCodeFixTest<TAnalyzer, TCodeFix, XUnitVerifier>
         {
+            /// <summary>
+            /// By default, the compiler reports diagnostics for nullable reference types at
+            /// <see cref="DiagnosticSeverity.Warning"/>, and the analyzer test framework defaults to only validating
+            /// diagnostics at <see cref="DiagnosticSeverity.Error"/>. This map contains all compiler diagnostic IDs
+            /// related to nullability mapped to <see cref="ReportDiagnostic.Error"/>, which is then used to enable all
+            /// of these warnings for default validation during analyzer and code fix tests.
+            /// </summary>
             private static readonly ImmutableDictionary<string, ReportDiagnostic> s_nullableWarnings = GetNullableWarningsFromCompiler();
 
             public Test()
@@ -60,8 +67,16 @@ public Test()
                 return nullableWarnings;
             }
 
+            /// <summary>
+            /// Gets or sets the language version to use for the test. The default value is
+            /// <see cref="LanguageVersion.CSharp8"/>.
+            /// </summary>
             public LanguageVersion LanguageVersion { get; set; } = LanguageVersion.CSharp8;
 
+            /// <summary>
+            /// Gets a collection of options to apply to <see cref="Solution.Options"/> for testing. Values may be added
+            /// using a collection initializer.
+            /// </summary>
             public OptionsCollection Options { get; } = new OptionsCollection(LanguageNames.CSharp);
 
             protected override AnalyzerOptions GetAnalyzerOptions(Project project)

src/EditorFeatures/TestUtilities/CodeActions/CSharpCodeFixVerifier`2.cs

@@ -15,18 +15,30 @@ public static partial class CSharpCodeFixVerifier<TAnalyzer, TCodeFix>
         where TAnalyzer : DiagnosticAnalyzer, new()
         where TCodeFix : CodeFixProvider, new()
     {
+        /// <inheritdoc cref="CodeFixVerifier{TAnalyzer, TCodeFix, TTest, TVerifier}.Diagnostic()"/>
         public static DiagnosticResult Diagnostic()
             => CSharpCodeFixVerifier<TAnalyzer, TCodeFix, XUnitVerifier>.Diagnostic();
 
+        /// <inheritdoc cref="CodeFixVerifier{TAnalyzer, TCodeFix, TTest, TVerifier}.Diagnostic(string)"/>
         public static DiagnosticResult Diagnostic(string diagnosticId)
             => CSharpCodeFixVerifier<TAnalyzer, TCodeFix, XUnitVerifier>.Diagnostic(diagnosticId);
 
+        /// <inheritdoc cref="CodeFixVerifier{TAnalyzer, TCodeFix, TTest, TVerifier}.Diagnostic(DiagnosticDescriptor)"/>
         public static DiagnosticResult Diagnostic(DiagnosticDescriptor descriptor)
             => CSharpCodeFixVerifier<TAnalyzer, TCodeFix, XUnitVerifier>.Diagnostic(descriptor);
 
+        /// <summary>
+        /// Verify standard properties of <typeparamref name="TAnalyzer"/>.
+        /// </summary>
+        /// <remarks>
+        /// This validation method is largely specific to dotnet/roslyn scenarios.
+        /// </remarks>
+        /// <param name="verifyHelpLink"><see langword="true"/> to verify <see cref="DiagnosticDescriptor.HelpLinkUri"/>
+        /// property of supported diagnostics; otherwise, <see langword="false"/> to skip this validation.</param>
         public static void VerifyStandardProperties(bool verifyHelpLink = false)
             => CodeFixVerifierHelper.VerifyStandardProperties(new TAnalyzer(), verifyHelpLink);
 
+        /// <inheritdoc cref="CodeFixVerifier{TAnalyzer, TCodeFix, TTest, TVerifier}.VerifyAnalyzerAsync(string, DiagnosticResult[])"/>
         public static async Task VerifyAnalyzerAsync(string source, params DiagnosticResult[] expected)
         {
             var test = new Test
@@ -38,12 +50,15 @@ public static async Task VerifyAnalyzerAsync(string source, params DiagnosticRes
             await test.RunAsync();
         }
 
+        /// <inheritdoc cref="CodeFixVerifier{TAnalyzer, TCodeFix, TTest, TVerifier}.VerifyCodeFixAsync(string, string)"/>
         public static async Task VerifyCodeFixAsync(string source, string fixedSource)
             => await VerifyCodeFixAsync(source, DiagnosticResult.EmptyDiagnosticResults, fixedSource);
 
+        /// <inheritdoc cref="CodeFixVerifier{TAnalyzer, TCodeFix, TTest, TVerifier}.VerifyCodeFixAsync(string, DiagnosticResult, string)"/>
         public static async Task VerifyCodeFixAsync(string source, DiagnosticResult expected, string fixedSource)
             => await VerifyCodeFixAsync(source, new[] { expected }, fixedSource);
 
+        /// <inheritdoc cref="CodeFixVerifier{TAnalyzer, TCodeFix, TTest, TVerifier}.VerifyCodeFixAsync(string, DiagnosticResult[], string)"/>
         public static async Task VerifyCodeFixAsync(string source, DiagnosticResult[] expected, string fixedSource)
         {
             var test = new Test

src/EditorFeatures/TestUtilities/CodeActions/VisualBasicCodeFixVerifier`2+Test.cs

@@ -38,8 +38,16 @@ public Test()
                 });
             }
 
+            /// <summary>
+            /// Gets or sets the language version to use for the test. The default value is
+            /// <see cref="LanguageVersion.VisualBasic16"/>.
+            /// </summary>
             public LanguageVersion LanguageVersion { get; set; } = LanguageVersion.VisualBasic16;
 
+            /// <summary>
+            /// Gets a collection of options to apply to <see cref="Solution.Options"/> for testing. Values may be added
+            /// using a collection initializer.
+            /// </summary>
             public OptionsCollection Options { get; } = new OptionsCollection(LanguageNames.VisualBasic);
 
             protected override AnalyzerOptions GetAnalyzerOptions(Project project)

src/EditorFeatures/TestUtilities/CodeActions/VisualBasicCodeFixVerifier`2.cs

@@ -15,18 +15,30 @@ public static partial class VisualBasicCodeFixVerifier<TAnalyzer, TCodeFix>
         where TAnalyzer : DiagnosticAnalyzer, new()
         where TCodeFix : CodeFixProvider, new()
     {
+        /// <inheritdoc cref="CodeFixVerifier{TAnalyzer, TCodeFix, TTest, TVerifier}.Diagnostic()"/>
         public static DiagnosticResult Diagnostic()
             => VisualBasicCodeFixVerifier<TAnalyzer, TCodeFix, XUnitVerifier>.Diagnostic();
 
+        /// <inheritdoc cref="CodeFixVerifier{TAnalyzer, TCodeFix, TTest, TVerifier}.Diagnostic(string)"/>
         public static DiagnosticResult Diagnostic(string diagnosticId)
             => VisualBasicCodeFixVerifier<TAnalyzer, TCodeFix, XUnitVerifier>.Diagnostic(diagnosticId);
 
+        /// <inheritdoc cref="CodeFixVerifier{TAnalyzer, TCodeFix, TTest, TVerifier}.Diagnostic(DiagnosticDescriptor)"/>
         public static DiagnosticResult Diagnostic(DiagnosticDescriptor descriptor)
             => VisualBasicCodeFixVerifier<TAnalyzer, TCodeFix, XUnitVerifier>.Diagnostic(descriptor);
 
+        /// <summary>
+        /// Verify standard properties of <typeparamref name="TAnalyzer"/>.
+        /// </summary>
+        /// <remarks>
+        /// This validation method is largely specific to dotnet/roslyn scenarios.
+        /// </remarks>
+        /// <param name="verifyHelpLink"><see langword="true"/> to verify <see cref="DiagnosticDescriptor.HelpLinkUri"/>
+        /// property of supported diagnostics; otherwise, <see langword="false"/> to skip this validation.</param>
         public static void VerifyStandardProperties(bool verifyHelpLink = false)
             => CodeFixVerifierHelper.VerifyStandardProperties(new TAnalyzer(), verifyHelpLink);
 
+        /// <inheritdoc cref="CodeFixVerifier{TAnalyzer, TCodeFix, TTest, TVerifier}.VerifyAnalyzerAsync(string, DiagnosticResult[])"/>
         public static async Task VerifyAnalyzerAsync(string source, params DiagnosticResult[] expected)
         {
             var test = new Test
@@ -38,12 +50,15 @@ public static async Task VerifyAnalyzerAsync(string source, params DiagnosticRes
             await test.RunAsync();
         }
 
+        /// <inheritdoc cref="CodeFixVerifier{TAnalyzer, TCodeFix, TTest, TVerifier}.VerifyCodeFixAsync(string, string)"/>
         public static async Task VerifyCodeFixAsync(string source, string fixedSource)
             => await VerifyCodeFixAsync(source, DiagnosticResult.EmptyDiagnosticResults, fixedSource);
 
+        /// <inheritdoc cref="CodeFixVerifier{TAnalyzer, TCodeFix, TTest, TVerifier}.VerifyCodeFixAsync(string, DiagnosticResult, string)"/>
         public static async Task VerifyCodeFixAsync(string source, DiagnosticResult expected, string fixedSource)
             => await VerifyCodeFixAsync(source, new[] { expected }, fixedSource);
 
+        /// <inheritdoc cref="CodeFixVerifier{TAnalyzer, TCodeFix, TTest, TVerifier}.VerifyCodeFixAsync(string, DiagnosticResult[], string)"/>
         public static async Task VerifyCodeFixAsync(string source, DiagnosticResult[] expected, string fixedSource)
         {
             var test = new Test