Add option to request preview version for nanoCLR

poc/TestOfTestFramework/nano.runsettings

@@ -13,5 +13,6 @@
        <CLRVersion></CLRVersion><!--Specify the nanoCLR version to use. If not specified, the latest available will be used. -->
        <PathToLocalCLRInstance></PathToLocalCLRInstance><!--Specify the path to a local nanoCLR instance. If not specified, the default one installed with nanoclr CLR witll be used. -->
        <RunnerExtraArguments></RunnerExtraArguments><!--Specify extra arguments to pass to the test runner. -->
+       <UsePreviewClr>False</UsePreviewClr><!--Set to true to use the preview version of the nanoCLR. -->
    </nanoFrameworkAdapter>
 </RunSettings>

poc/TestOfTestFrameworkByReference/nano.runsettings

@@ -14,5 +14,6 @@
        <Logging>None</Logging>
        <IsRealHardware>False</IsRealHardware>
        <RunnerExtraArguments></RunnerExtraArguments><!--Specify extra arguments to pass to the test runner. -->
+       <UsePreviewClr>False</UsePreviewClr><!--Set to true to use the preview version of the nanoCLR. -->
    </nanoFrameworkAdapter>
 </RunSettings>

source/TestAdapter/Executor.cs

@@ -670,6 +670,7 @@ private async Task<List<TestResult>> RunTestOnEmulatorAsync(
             {
                 NanoCLRHelper.UpdateNanoCLRInstance(
                     _settings.CLRVersion,
+                    _settings.UsePreviewClr,
                     _logger);
             }
 

source/TestAdapter/NanoCLRHelper.cs

@@ -163,8 +163,15 @@ public static bool InstallNanoClr(LogMessenger logger)
             return NanoClrIsInstalled;
         }
 
+        /// <summary>
+        /// Update the nanoCLR instance.
+        /// </summary>
+        /// <param name="clrVersion">Specific version to use.</param>
+        /// <param name="usePreview"><see langword="true"/> to use preview version, <see langword="false"/> to use stable version.</param>
+        /// <param name="logger">The logger to use to log messages.</param>
         public static void UpdateNanoCLRInstance(
             string clrVersion,
+            bool usePreview,
             LogMessenger logger)
         {
             logger.LogMessage(
@@ -173,17 +180,26 @@ public static void UpdateNanoCLRInstance(
 
             string arguments = "instance --update";
 
-            if (!string.IsNullOrEmpty(clrVersion))
+            // use preview parameter has precedence over the version
+            if (usePreview)
+            {
+                arguments += " --preview";
+            }
+            else
             {
-                arguments += $" --clrversion {clrVersion}";
+                // if no preview, check if we have a version to use
+                if (!string.IsNullOrEmpty(clrVersion))
+                {
+                    arguments += $" --version {clrVersion}";
+                }
             }
 
             Command cmd = Cli.Wrap("nanoclr")
                 .WithArguments(arguments)
                 .WithValidation(CommandResultValidation.None);
 
             // setup cancellation token with a timeout of 1 minute
-            using (var cts = new CancellationTokenSource(TimeSpan.FromMinutes(1)))
+            using (CancellationTokenSource cts = new CancellationTokenSource(TimeSpan.FromMinutes(1)))
             {
                 BufferedCommandResult cliResult = cmd.ExecuteBufferedAsync(cts.Token).Task.Result;
 

source/TestAdapter/Settings.cs

@@ -31,6 +31,14 @@ public class Settings
         /// </summary>
         public string CLRVersion { get; set; } = string.Empty;
 
+        /// <summary>
+        /// <see langword="true"/> to use a preview version of the nanoCLR instance.
+        /// </summary>
+        /// <remarks>
+        /// Set to <see langword="false"/>, or don't set the property, to use the latest stable version.
+        /// </remarks>
+        public bool UsePreviewClr { get; set; } = false;
+
         /// <summary>
         /// Level of logging for Unit Test execution.
         /// </summary>
@@ -90,6 +98,12 @@ public static Settings Extract(XmlNode node)
                 {
                     settings.RunnerExtraArguments = runnerExtraArguments.Value;
                 }
+
+                XmlNode usePreviewClr = node.SelectSingleNode(nameof(UsePreviewClr))?.FirstChild;
+                if (usePreviewClr != null && usePreviewClr.NodeType == XmlNodeType.Text)
+                {
+                    settings.UsePreviewClr = usePreviewClr.Value.Equals("true", StringComparison.CurrentCultureIgnoreCase);
+                }
             }
 
             return settings;