change messaging around Windows (#8549)

packages/flutter_tools/lib/src/commands/test.dart

@@ -156,6 +156,13 @@ class TestCommand extends FlutterCommand {
 
   @override
   Future<Null> runCommand() async {
+    if (platform.isWindows) {
+      throwToolExit(
+          'The test command is currently not supported on Windows: '
+          'https://github.com/flutter/flutter/issues/8516'
+      );
+    }
+
     List<String> testArgs = <String>[];
 
     commandValidator();

packages/flutter_tools/lib/src/doctor.dart

@@ -224,15 +224,6 @@ class _FlutterValidator extends DoctorValidator {
     messages.add(new ValidationMessage('Engine revision ${version.engineRevisionShort}'));
     messages.add(new ValidationMessage('Tools Dart version ${version.dartSdkVersion}'));
 
-    if (platform.isWindows) {
-      valid = ValidationType.missing;
-
-      messages.add(new ValidationMessage.error(
-        'Flutter tools are not (yet) supported on Windows: '
-        'https://github.com/flutter/flutter/issues/138.'
-      ));
-    }
-
     return new ValidationResult(valid, messages,
       statusInfo: 'on ${osName()}, channel ${version.channel}');
   }