Let's avoid switching to C# 6 for now.

ICSharpCode.Decompiler/Tests/FSharpPatterns/FSharpPatternTests.cs

@@ -5,7 +5,6 @@ using System.Linq;
 using System.Reflection;
 using System.Text;
 using System.Threading.Tasks;
-using static ICSharpCode.Decompiler.Tests.FSharpPatterns.TestHelpers;
 
 namespace ICSharpCode.Decompiler.Tests.FSharpPatterns
 {
@@ -15,17 +14,17 @@ namespace ICSharpCode.Decompiler.Tests.FSharpPatterns
 		[Test]
 		public void FSharpUsingDecompilesToCSharpUsing_Debug()
 		{
-			var ilCode = FuzzyReadResource("FSharpUsing.fs.Debug.il");
-			var csharpCode = FuzzyReadResource("FSharpUsing.fs.Debug.cs");
-			RunIL(ilCode, csharpCode);
+			var ilCode = TestHelpers.FuzzyReadResource("FSharpUsing.fs.Debug.il");
+			var csharpCode = TestHelpers.FuzzyReadResource("FSharpUsing.fs.Debug.cs");
+			TestHelpers.RunIL(ilCode, csharpCode);
 		}
 
 		[Test]
 		public void FSharpUsingDecompilesToCSharpUsing_Release()
 		{
-			var ilCode = FuzzyReadResource("FSharpUsing.fs.Release.il");
-			var csharpCode = FuzzyReadResource("FSharpUsing.fs.Release.cs");
-			RunIL(ilCode, csharpCode);
+			var ilCode = TestHelpers.FuzzyReadResource("FSharpUsing.fs.Release.il");
+			var csharpCode = TestHelpers.FuzzyReadResource("FSharpUsing.fs.Release.cs");
+			TestHelpers.RunIL(ilCode, csharpCode);
 		}
 	}
 }

ICSharpCode.Decompiler/Tests/FSharpPatterns/TestHelpers.cs

@@ -20,7 +20,7 @@ namespace ICSharpCode.Decompiler.Tests.FSharpPatterns
 		{
 			var asm = Assembly.GetExecutingAssembly();
 			var allResources = asm.GetManifestResourceNames();
-			var fullResourceName = allResources.Single(r => r.ToLowerInvariant().EndsWith(resourceName.ToLowerInvariant()));
+			var fullResourceName = allResources.Single(r => r.EndsWith(resourceName, StringComparison.OrdinalIgnoreCase));
 			return new StreamReader(asm.GetManifestResourceStream(fullResourceName)).ReadToEnd();
 		}
 
@@ -33,7 +33,7 @@ namespace ICSharpCode.Decompiler.Tests.FSharpPatterns
 			File.WriteAllText(sourceFile, source);
 			var asmFile = Path.ChangeExtension(sourceFile, ".dll");
 			var sscs = new Microsoft.FSharp.Compiler.SimpleSourceCodeServices.SimpleSourceCodeServices();
-			var result = sscs.Compile(new[] { "fsc.exe", "--debug:full", $"--optimize{(optimize ? "+" : "-")}", "--target:library", "-o", asmFile, sourceFile });
+			var result = sscs.Compile(new[] { "fsc.exe", "--debug:full", "--optimize" + (optimize ? "+" : "-"), "--target:library", "-o", asmFile, sourceFile });
 			File.Delete(sourceFile);
 			Assert.AreEqual(0, result.Item1.Length);
 			Assert.AreEqual(0, result.Item2);
@@ -54,7 +54,7 @@ namespace ICSharpCode.Decompiler.Tests.FSharpPatterns
 			File.WriteAllText(sourceFile, source);
 			var asmFile = Path.ChangeExtension(sourceFile, ".dll");
 
-			var args = $"{sourceFile} /dll /debug /output:{asmFile}";
+			var args = string.Format("{0} /dll /debug /output:{1}", sourceFile, asmFile);
 			using (var proc = Process.Start(new ProcessStartInfo(ilasm.Value, args) { UseShellExecute = false,  }))
 			{
 				proc.WaitForExit();
@@ -91,8 +91,9 @@ namespace ICSharpCode.Decompiler.Tests.FSharpPatterns
 
 				// the F# assembly contains a namespace `<StartupCode$tmp6D55>` where the part after tmp is randomly generated.
 				// remove this from the ast to simplify the diff
-				var startupCodeNode = decompiler.SyntaxTree.Children.SingleOrDefault(d => (d as NamespaceDeclaration)?.Name?.StartsWith("<StartupCode$") ?? false);
-				startupCodeNode?.Remove();
+				var startupCodeNode = decompiler.SyntaxTree.Children.OfType<NamespaceDeclaration>().SingleOrDefault(d => d.Name.StartsWith("<StartupCode$", StringComparison.Ordinal));
+				if (startupCodeNode != null)
+					startupCodeNode.Remove();
 
 				decompiler.GenerateCode(new PlainTextOutput(output));
 				var fullCSharpCode = output.ToString();

ICSharpCode.Decompiler/Tests/FSharpPatterns/ToolLocator.cs

@@ -19,19 +19,19 @@ namespace ICSharpCode.Decompiler.Tests.FSharpPatterns
 		{
 			string[] windowsSdkPaths = new[]
 			{
-	@"Microsoft SDKs\Windows\v8.0A\bin\NETFX 4.0 Tools\",
-	@"Microsoft SDKs\Windows\v8.0A\bin\",
-	@"Microsoft SDKs\Windows\v8.0\bin\NETFX 4.0 Tools\",
-	@"Microsoft SDKs\Windows\v8.0\bin\",
-	@"Microsoft SDKs\Windows\v7.1A\bin\NETFX 4.0 Tools\",
-	@"Microsoft SDKs\Windows\v7.1A\bin\",
-	@"Microsoft SDKs\Windows\v7.0A\bin\NETFX 4.0 Tools\",
-	@"Microsoft SDKs\Windows\v7.0A\bin\",
-	@"Microsoft SDKs\Windows\v6.1A\bin\",
-	@"Microsoft SDKs\Windows\v6.0A\bin\",
-	@"Microsoft SDKs\Windows\v6.0\bin\",
-	@"Microsoft.NET\FrameworkSDK\bin"
-  };
+				@"Microsoft SDKs\Windows\v8.0A\bin\NETFX 4.0 Tools\",
+				@"Microsoft SDKs\Windows\v8.0A\bin\",
+				@"Microsoft SDKs\Windows\v8.0\bin\NETFX 4.0 Tools\",
+				@"Microsoft SDKs\Windows\v8.0\bin\",
+				@"Microsoft SDKs\Windows\v7.1A\bin\NETFX 4.0 Tools\",
+				@"Microsoft SDKs\Windows\v7.1A\bin\",
+				@"Microsoft SDKs\Windows\v7.0A\bin\NETFX 4.0 Tools\",
+				@"Microsoft SDKs\Windows\v7.0A\bin\",
+				@"Microsoft SDKs\Windows\v6.1A\bin\",
+				@"Microsoft SDKs\Windows\v6.0A\bin\",
+				@"Microsoft SDKs\Windows\v6.0\bin\",
+				@"Microsoft.NET\FrameworkSDK\bin"
+			};
 
 			foreach (var possiblePath in windowsSdkPaths)
 			{
@@ -71,9 +71,9 @@ namespace ICSharpCode.Decompiler.Tests.FSharpPatterns
 		{
 			string[] frameworkPaths = new[]
 			{
-	@"Microsoft.NET\Framework\v4.0.30319",
-	@"Microsoft.NET\Framework\v2.0.50727"
-  };
+				@"Microsoft.NET\Framework\v4.0.30319",
+				@"Microsoft.NET\Framework\v2.0.50727"
+			};
 
 			foreach (var possiblePath in frameworkPaths)
 			{