Move unicode tests to utf package.

tests/corelib/unicode2_test.dart

+// Copyright (c) 2012, 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.
+
+import 'package:expect/expect.dart';
+
+const String testPhrase =
+    "The quick brown fox jumps over the lazy dog.";
+
+const List<int> testCodepoints = const<int> [
+    84, 104, 101, 32, 113, 117, 105, 99, 107, 32, 98, 114, 111, 119, 110,
+    32, 102, 111, 120, 32, 106, 117, 109, 112, 115, 32, 111, 118, 101, 114,
+    32, 116, 104, 101, 32, 108, 97, 122, 121, 32, 100, 111, 103, 46];
+
+main() {
+  testCodepointsToString();
+  testStringCharCodes();
+  testEmptyStringFromCharCodes();
+  testEmptyStringCharCodes();
+}
+
+void testStringCharCodes() {
+  Expect.listEquals(testCodepoints, testPhrase.codeUnits);
+}
+
+void testCodepointsToString() {
+  Expect.stringEquals(testPhrase, new String.fromCharCodes(testCodepoints));
+}
+
+void testEmptyStringFromCharCodes() {
+  Expect.stringEquals("", new String.fromCharCodes(<int>[]));
+}
+
+void testEmptyStringCharCodes() {
+  Expect.listEquals([], "".codeUnits);
+}