Consistently use "OS" rather than "Os" in identifiers.

lib/src/utils.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library unittest.utils;
 
 import 'dart:async';
 
 import 'package:path/path.dart' as p;
 import 'package:stack_trace/stack_trace.dart';
 
 import 'backend/operating_system.dart';
 
 /// A typedef for a possibly-asynchronous function.
 ///
 /// The return type should only ever by [Future] or void.
 typedef AsyncFunction();
 
 /// A regular expression to match the exception prefix that some exceptions'
 /// [Object.toString] values contain.
 final _exceptionPrefix = new RegExp(r'^([A-Z][a-zA-Z]*)?(Exception|Error): ');
 
 /// Directories that are specific to OS X.
 ///
-/// This is used to try to distinguish OS X and Linux in [currentOsGuess].
-final _macOsDirectories = new Set<String>.from([
+/// This is used to try to distinguish OS X and Linux in [currentOSGuess].
+final _macOSDirectories = new Set<String>.from([
   "/Applications",
   "/Library",
   "/Network",
   "/System",
   "/Users"
 ]);
 
 /// Returns the best guess for the current operating system without using
 /// `dart:io`.
 ///
 /// This is useful for running test files directly and skipping tests as
 /// appropriate. The only OS-specific information we have is the current path,
 /// which we try to use to figure out the OS.
-final OperatingSystem currentOsGuess = (() {
+final OperatingSystem currentOSGuess = (() {
   if (p.style == p.Style.url) return OperatingSystem.none;
   if (p.style == p.Style.windows) return OperatingSystem.windows;
-  if (_macOsDirectories.any(p.current.startsWith)) return OperatingSystem.macOs;
+  if (_macOSDirectories.any(p.current.startsWith)) return OperatingSystem.macOS;
   return OperatingSystem.linux;
 })();
 
 /// Get a string description of an exception.
 ///
 /// Many exceptions include the exception class name at the beginning of their
 /// [toString], so we remove that if it exists.
 String getErrorMessage(error) =>
   error.toString().replaceFirst(_exceptionPrefix, '');
 
@@ skipping 80 matching lines @@
 
   // Otherwise truncate to return the trailing text, but attempt to start at
   // the beginning of a word.
   var result = text.substring(text.length - maxLength + 4);
   var firstSpace = result.indexOf(' ');
   if (firstSpace > 0) {
     result = result.substring(firstSpace);
   }
   return '...$result';
 }