add tests

packages/flutter_tools/test/adb_test.dart

+// Copyright 2015 The Chromium Authors. 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:flutter_tools/src/android/adb.dart';
+import 'package:test/test.dart';
+
+main() => defineTests();
+
+defineTests() {
+  Adb adb = new Adb('adb');
+
+  // We only test the [Adb] class is we're able to locate the adb binary.
+  if (!adb.exists())
+    return;
+
+  group('adb', () {
+    test('getVersion', () {
+      expect(adb.getVersion(), isNotEmpty);
+    });
+
+    test('getServerVersion', () async {
+      adb.startServer();
+
+      String version = await adb.getServerVersion();
+      expect(version, isNotEmpty);
+    });
+
+    test('listDevices', () async {
+      adb.startServer();
+
+      List<AdbDevice> devices = await adb.listDevices();
+
+      // Any result is ok.
+      expect(devices, isList);
+    });
+  });
+}