diff --git a/src/PowerShellEditorServices/Services/Analysis/AnalysisService.cs b/src/PowerShellEditorServices/Services/Analysis/AnalysisService.cs
index 73e5cfa27..514e629a5 100644
--- a/src/PowerShellEditorServices/Services/Analysis/AnalysisService.cs
+++ b/src/PowerShellEditorServices/Services/Analysis/AnalysisService.cs
@@ -122,7 +122,7 @@ public AnalysisService(
         /// <summary>
         /// The analysis engine to use for running script analysis.
         /// </summary>
-        private PssaCmdletAnalysisEngine AnalysisEngine => _analysisEngineLazy?.Value;
+        internal PssaCmdletAnalysisEngine AnalysisEngine => _analysisEngineLazy?.Value;
 
         /// <summary>
         /// Sets up a script analysis run, eventually returning the result.
@@ -346,7 +346,7 @@ private void ClearOpenFileMarkers()
             }
         }
 
-        private async Task DelayThenInvokeDiagnosticsAsync(ScriptFile[] filesToAnalyze, CancellationToken cancellationToken)
+        internal async Task DelayThenInvokeDiagnosticsAsync(ScriptFile[] filesToAnalyze, CancellationToken cancellationToken)
         {
             if (cancellationToken.IsCancellationRequested)
             {
@@ -409,7 +409,7 @@ private void PublishScriptDiagnostics(ScriptFile scriptFile, IReadOnlyList<Scrip
                 diagnostics[i] = diagnostic;
             }
 
-            _languageServer.TextDocument.PublishDiagnostics(new PublishDiagnosticsParams
+            _languageServer?.TextDocument.PublishDiagnostics(new PublishDiagnosticsParams
             {
                 Uri = scriptFile.DocumentUri,
                 Diagnostics = new Container<Diagnostic>(diagnostics)
diff --git a/test/PowerShellEditorServices.Test/Debugging/DebugServiceTests.cs b/test/PowerShellEditorServices.Test/Debugging/DebugServiceTests.cs
index d0f1f0ef0..02a5a23bc 100644
--- a/test/PowerShellEditorServices.Test/Debugging/DebugServiceTests.cs
+++ b/test/PowerShellEditorServices.Test/Debugging/DebugServiceTests.cs
@@ -532,8 +532,8 @@ public async Task DebuggerBreaksInUntitledScript()
             const string scriptPath = "untitled:Untitled-1";
             Assert.True(ScriptFile.IsUntitledPath(scriptPath));
             ScriptFile scriptFile = workspace.GetFileBuffer(scriptPath, contents);
-            Assert.Equal(scriptFile.DocumentUri, scriptPath);
-            Assert.Equal(scriptFile.Contents, contents);
+            Assert.Equal(scriptPath, scriptFile.DocumentUri);
+            Assert.Equal(contents, scriptFile.Contents);
             Assert.True(workspace.TryGetFile(scriptPath, out ScriptFile _));
 
             await debugService.SetCommandBreakpointsAsync(
diff --git a/test/PowerShellEditorServices.Test/Extensions/ExtensionCommandTests.cs b/test/PowerShellEditorServices.Test/Extensions/ExtensionCommandTests.cs
index b6fbd881e..430687f93 100644
--- a/test/PowerShellEditorServices.Test/Extensions/ExtensionCommandTests.cs
+++ b/test/PowerShellEditorServices.Test/Extensions/ExtensionCommandTests.cs
@@ -72,8 +72,8 @@ await psesHost.ExecutePSCommandAsync(
                 CancellationToken.None).ConfigureAwait(true);
 
             Assert.NotNull(commandAdded);
-            Assert.Equal(commandAdded.Name, commandName);
-            Assert.Equal(commandAdded.DisplayName, commandDisplayName);
+            Assert.Equal(commandName, commandAdded.Name);
+            Assert.Equal(commandDisplayName, commandAdded.DisplayName);
 
             // Invoke the command
             await extensionCommandService.InvokeCommandAsync(commandName, editorContext).ConfigureAwait(true);
diff --git a/test/PowerShellEditorServices.Test/Services/Symbols/PSScriptAnalyzerTests.cs b/test/PowerShellEditorServices.Test/Services/Symbols/PSScriptAnalyzerTests.cs
index 05f069f2c..9e8c00dde 100644
--- a/test/PowerShellEditorServices.Test/Services/Symbols/PSScriptAnalyzerTests.cs
+++ b/test/PowerShellEditorServices.Test/Services/Symbols/PSScriptAnalyzerTests.cs
@@ -2,11 +2,11 @@
 // Licensed under the MIT License.
 
 using System.Linq;
+using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.Extensions.Logging.Abstractions;
 using Microsoft.PowerShell.EditorServices.Hosting;
 using Microsoft.PowerShell.EditorServices.Services;
-using Microsoft.PowerShell.EditorServices.Services.Analysis;
 using Microsoft.PowerShell.EditorServices.Services.TextDocument;
 using Microsoft.PowerShell.EditorServices.Test;
 using Xunit;
@@ -16,13 +16,15 @@ namespace PowerShellEditorServices.Test.Services.Symbols
     [Trait("Category", "PSScriptAnalyzer")]
     public class PSScriptAnalyzerTests
     {
+        private readonly WorkspaceService workspaceService = new(NullLoggerFactory.Instance);
         private readonly AnalysisService analysisService;
+        private const string script = "function Get-Widgets {}";
 
         public PSScriptAnalyzerTests() => analysisService = new(
             NullLoggerFactory.Instance,
             languageServer: null,
             configurationService: null,
-            workspaceService: null,
+            workspaceService: workspaceService,
             new HostStartupInfo(
                 name: "",
                 profileId: "",
@@ -39,11 +41,13 @@ public class PSScriptAnalyzerTests
                 bundledModulePath: PsesHostFactory.BundledModulePath));
 
         [Fact]
-        public async Task CanLoadPSScriptAnalyzer()
+        public async Task CanLoadPSScriptAnalyzerAsync()
         {
-            PssaCmdletAnalysisEngine engine = analysisService.InstantiateAnalysisEngine();
-            Assert.NotNull(engine);
-            ScriptFileMarker[] violations = await engine.AnalyzeScriptAsync("function Get-Widgets {}").ConfigureAwait(true);
+            ScriptFileMarker[] violations = await analysisService
+                .AnalysisEngine
+                .AnalyzeScriptAsync(script)
+                .ConfigureAwait(true);
+
             Assert.Collection(violations,
             (actual) =>
             {
@@ -54,5 +58,23 @@ public async Task CanLoadPSScriptAnalyzer()
                 Assert.Equal("PSScriptAnalyzer", actual.Source);
             });
         }
+
+        [Fact]
+        public async Task DoesNotDuplicateScriptMarkersAsync()
+        {
+            ScriptFile scriptFile = workspaceService.GetFileBuffer("untitled:Untitled-1", script);
+            ScriptFile[] scriptFiles = { scriptFile };
+
+            await analysisService
+                .DelayThenInvokeDiagnosticsAsync(scriptFiles, CancellationToken.None)
+                .ConfigureAwait(true);
+            Assert.Single(scriptFile.DiagnosticMarkers);
+
+            // This is repeated to test that the markers are not duplicated.
+            await analysisService
+                .DelayThenInvokeDiagnosticsAsync(scriptFiles, CancellationToken.None)
+                .ConfigureAwait(true);
+            Assert.Single(scriptFile.DiagnosticMarkers);
+        }
     }
 }