Add code action equivalence key validation in test framework

Fixes #44553

src/EditorFeatures/DiagnosticsTestUtilities/CodeActions/AbstractCodeActionOrUserDiagnosticTest.cs

@@ -19,6 +19,8 @@
 using Roslyn.Utilities;
 using Roslyn.Test.Utilities;
 using Xunit;
+using Microsoft.CodeAnalysis.CodeFixes;
+using Microsoft.CodeAnalysis.CodeRefactorings;
 
 #if CODE_STYLE
 using System.Diagnostics;
@@ -681,6 +683,46 @@ static void VerifyExpectedDocumentText(string expected, string actual)
         protected virtual ImmutableArray<CodeAction> MassageActions(ImmutableArray<CodeAction> actions)
             => actions;
 
+        internal static void VerifyCodeActionsRegisteredByProvider(List<CodeFix> fixes)
+        {
+            var diagnosticsAndEquivalenceKeyToTitleMap = new Dictionary<(Diagnostic diagnostic, string equivalenceKey), string>();
+            foreach (var fix in fixes)
+            {
+                var codeAction = fix.Action;
+                foreach (var diagnostic in fix.Diagnostics)
+                {
+                    var key = (diagnostic, codeAction.EquivalenceKey);
+                    var existingTitle = diagnosticsAndEquivalenceKeyToTitleMap.GetOrAdd(key, _ => codeAction.Title);
+                    if (existingTitle != codeAction.Title)
+                    {
+                        Assert.False(true, @$"Expected different 'CodeAction.EquivalenceKey' for code actions registered for same diagnostic:
+- Title 1: '{codeAction.Title}'
+- Title 2: '{existingTitle}'
+- Shared equivalence key: '{codeAction.EquivalenceKey ?? "<null>"}'");
+
+                    }
+                }
+            }
+        }
+
+        internal static void VerifyCodeActionsRegisteredByProvider(CodeRefactoring refactorings)
+        {
+            var applicableSpanAndEquivalenceKeyToTitleMap = new Dictionary<(TextSpan applicableToSpan, string equivalenceKey), string>();
+            foreach (var (codeAction, applicableToSpan) in refactorings.CodeActions)
+            {
+                var key = (applicableToSpan ?? default, codeAction.EquivalenceKey);
+                var existingTitle = applicableSpanAndEquivalenceKeyToTitleMap.GetOrAdd(key, _ => codeAction.Title);
+                if (existingTitle != codeAction.Title)
+                {
+                    Assert.False(true, @$"Expected different 'CodeAction.EquivalenceKey' for code actions registered for same applicable span:
+- Title 1: '{codeAction.Title}'
+- Title 2: '{existingTitle}'
+- Shared equivalence key: '{codeAction.EquivalenceKey ?? "<null>"}'");
+
+                }
+            }
+        }
+
         protected static ImmutableArray<CodeAction> FlattenActions(ImmutableArray<CodeAction> codeActions)
         {
             return codeActions.SelectMany(a => a.NestedCodeActions.Length > 0

src/EditorFeatures/DiagnosticsTestUtilities/CodeActions/AbstractCodeActionTest.cs

@@ -70,6 +70,9 @@ protected override Task<ImmutableArray<Diagnostic>> GetDiagnosticsWorkerAsync(Te
 
             var result = actions.Count > 0 ? new CodeRefactoring(provider, actions.ToImmutable()) : null;
             actions.Free();
+
+            VerifyCodeActionsRegisteredByProvider(result);
+
             return result;
         }
 

src/EditorFeatures/DiagnosticsTestUtilities/Diagnostics/AbstractUserDiagnosticTest.cs

@@ -202,6 +202,8 @@ protected Document GetDocumentAndAnnotatedSpan(TestWorkspace workspace, out stri
                 await fixer.RegisterCodeFixesAsync(context);
             }
 
+            VerifyCodeActionsRegisteredByProvider(fixes);
+
             var actions = fixes.SelectAsArray(f => f.Action);
 
             actions = MassageActions(actions);