Add resource tests.

tests/corelib/file_resource_test.dart

+// Copyright (c) 2015, 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 "dart:io";
+
+const sampleText = "Sample text file.";
+
+main() async {
+  var file = await createFile();
+  var uri = new Uri.file(file.path);
+
+  var resource = new Resource(uri.toString());
+
+  if (resource.uri != uri) {
+    throw "Incorrect URI: ${resource.uri}";
+  }
+
+  var text = await resource.readAsString();
+  if (text != sampleText) {
+    throw "Incorrect reading of text file: $text";
+  }
+
+  var bytes = await resource.readAsBytes();
+  if (!compareBytes(bytes, sampleText.codeUnits)) {
+    throw "Incorrect reading of bytes: $bytes";
+  }
+
+  var streamBytes = [];
+  await for (var byteSlice in resource.openRead()) {
+    streamBytes.addAll(byteSlice);
+  }
+  if (!compareBytes(streamBytes, sampleText.codeUnits)) {
+    throw "Incorrect reading of bytes: $bytes";
+  }
+
+  await deleteFile(file);
+}
+
+/// Checks that [bytes] and [expectedBytes] have the same contents.
+bool compareBytes(bytes, expectedBytes) {
+  if (bytes.length != expectedBytes.length) return false;
+  for (int i = 0; i < expectedBytes.length; i++) {
+    if (bytes[i] != expectedBytes[i]) return false;
+  }
+  return true;
+}
+
+createFile() async {
+  var tempDir = await Directory.systemTemp.createTemp("sample");
+  var filePath = tempDir.path + Platform.pathSeparator + "sample.txt";
+  var file = new File(filePath);
+  await file.create();
+  await file.writeAsString(sampleText);
+  return file;
+}
+
+deleteFile(File file) async {
+  // Removes the file and the temporary directory it's in.
+  var parentDir = new Directory(file.path.substring(0,
+                                file.path.lastIndexOf(Platform.pathSeparator)));
+  await parentDir.delete(recursive: true);
+}