Respond to PR feedback

src/Compilers/CSharp/Test/CommandLine/CommandLineTestBase.cs

@@ -25,25 +25,22 @@ public abstract class CommandLineTestBase : CSharpTestBase
         public CommandLineTestBase()
         {
             WorkingDirectory = TempRoot.Root;
-            SdkDirectory = GetSdkDirectory(Temp);
+            SdkDirectory = getSdkDirectory(Temp);
             MscorlibFullPath = Path.Combine(SdkDirectory, "mscorlib.dll");
-        }
 
-        /// <summary>
-        /// This will return a directory which contains mscorlib for use in the compiler instances created for
-        /// this set of tests
-        /// </summary>
-        /// <returns></returns>
-        protected static string GetSdkDirectory(TempRoot temp)
-        {
-            if (ExecutionConditionUtil.IsCoreClr)
+            // This will return a directory which contains mscorlib for use in the compiler instances created for
+            // this set of tests
+            string getSdkDirectory(TempRoot temp)
             {
-                var dir = temp.CreateDirectory();
-                File.WriteAllBytes(Path.Combine(dir.Path, "mscorlib.dll"), TestResources.NetFX.net461.mscorlib);
-                return dir.Path;
+                if (ExecutionConditionUtil.IsCoreClr)
+                {
+                    var dir = temp.CreateDirectory();
+                    File.WriteAllBytes(Path.Combine(dir.Path, "mscorlib.dll"), TestResources.NetFX.net461.mscorlib);
+                    return dir.Path;
+                }
+
+                return RuntimeEnvironment.GetRuntimeDirectory();
             }
-
-            return RuntimeEnvironment.GetRuntimeDirectory();
         }
 
         internal CSharpCommandLineArguments DefaultParse(IEnumerable<string> args, string baseDirectory, string sdkDirectory = null, string additionalReferenceDirectories = null)

src/Compilers/Test/Utilities/CSharp/MockCSharpCompiler.cs

@@ -23,7 +23,7 @@ public MockCSharpCompiler(string responseFile, string workingDirectory, string[]
         public MockCSharpCompiler(string responseFile, BuildPaths buildPaths, string[] args, ImmutableArray<DiagnosticAnalyzer> analyzers = default, AnalyzerAssemblyLoader loader = null)
             : base(CSharpCommandLineParser.Default, responseFile, args, buildPaths, Environment.GetEnvironmentVariable("LIB"), loader ?? RuntimeUtilities.CreateAnalyzerAssemblyLoader())
         {
-            _analyzers = !analyzers.IsDefault ? analyzers : ImmutableArray<DiagnosticAnalyzer>.Empty;
+            _analyzers = analyzers.NullToEmpty();
         }
 
         private static BuildPaths CreateBuildPaths(string workingDirectory, string sdkDirectory = null) => RuntimeUtilities.CreateBuildPaths(workingDirectory, sdkDirectory);