Add some user-friendly utility functions to pkg/analyzer_experimental.

pkg/analyzer_experimental/test/utils.dart

Index: pkg/analyzer_experimental/test/utils.dart
diff --git a/pkg/analyzer_experimental/test/utils.dart b/pkg/analyzer_experimental/test/utils.dart
new file mode 100644
index 0000000000000000000000000000000000000000..62f99095be6943ebc4efeb7e7ca9e433cf12327b
--- /dev/null
+++ b/pkg/analyzer_experimental/test/utils.dart
@@ -0,0 +1,46 @@
+// 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 utils;
+
+import 'dart:io';
+
+import 'package:analyzer_experimental/analyzer.dart';
+import 'package:pathos/path.dart' as pathos;
+
+/// Returns the string representation of the [AnalyzerErrorGroup] thrown when
+/// parsing [contents] as a Dart file. If [contents] doesn't throw any errors,
+/// this will return null.
+///
+/// This replaces the filename in the error string with its basename, since the
+/// full path will vary from machine to machine. It also replaces the exception
+/// message with "..." to decouple these tests from the specific exception
+/// messages.
+String errorsForFile(String contents) {
+  return withTempDir((temp) {
+    var path = pathos.join(temp, 'test.dart');
+    new File(path).writeAsStringSync(contents);
+    try {
+      parseDartFile(path);
+    } on AnalyzerErrorGroup catch (e) {
+      return e.toString().replaceAllMapped(
+          new RegExp(r"^(Error on line \d+ of )([^:]+): .*$", multiLine: true),
+          (match) => match[1] + pathos.basename(match[2]) + ': ...');
+    }
+    return null;
+  });
+}
+
+/// Creates a temporary directory and passes its path to [fn]. Once [fn]
+/// completes, the temporary directory and all its contents will be deleted.
+///
+/// Returns the return value of [fn].
+dynamic withTempDir(fn(String path)) {
+  var tempDir = new Directory('').createTempSync().path;
+  try {
+    return fn(tempDir);
+  } finally {
+    new Directory(tempDir).deleteSync(recursive: true);
+  }
+}