Add some emulator tests

packages/flutter_tools/lib/src/emulator.dart

@@ -119,7 +119,7 @@ abstract class Emulator {
 
   final String id;
 
-  String get name;
+  String get name => id;
 
   @override
   int get hashCode => id.hashCode;

packages/flutter_tools/test/emulator_test.dart

+// Copyright 2018 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 'dart:async';
+
+import 'package:flutter_tools/src/emulator.dart';
+import 'package:test/test.dart';
+
+import 'src/context.dart';
+
+void main() {
+  group('EmulatorManager', () {
+    testUsingContext('getEmulators', () async {
+      // Test that EmulatorManager.getEmulators() doesn't throw.
+      final EmulatorManager emulatorManager = new EmulatorManager();
+      final List<Emulator> emulators = await emulatorManager.getAllAvailableEmulators().toList();
+      expect(emulators, isList);
+    });
+
+    testUsingContext('getEmulatorsById', () async {
+      final _MockEmulator emulator1 = new _MockEmulator('Nexus_5');
+      final _MockEmulator emulator2 = new _MockEmulator('Nexus_5X_API_27_x86');
+      final _MockEmulator emulator3 = new _MockEmulator('iOS Simulator');
+      final List<Emulator> emulators = <Emulator>[emulator1, emulator2, emulator3];
+      final EmulatorManager emulatorManager = new TestEmulatorManager(emulators);
+
+      Future<Null> expectEmulator(String id, List<Emulator> expected) async {
+        expect(await emulatorManager.getEmulatorsById(id).toList(), expected);
+      }
+      expectEmulator('Nexus_5', <Emulator>[emulator1]);
+      expectEmulator('Nexus_5X', <Emulator>[emulator2]);
+      expectEmulator('Nexus_5X_API_27_x86', <Emulator>[emulator2]);
+      expectEmulator('Nexus', <Emulator>[emulator1, emulator2]);
+      expectEmulator('iOS Simulator', <Emulator>[emulator3]);
+      expectEmulator('ios', <Emulator>[emulator3]);
+    });
+  });
+}
+
+class TestEmulatorManager extends EmulatorManager {
+  final List<Emulator> allEmulators;
+
+  TestEmulatorManager(this.allEmulators);
+
+  @override
+  Stream<Emulator> getAllAvailableEmulators() {
+    return new Stream<Emulator>.fromIterable(allEmulators);
+  }
+}
+
+class _MockEmulator extends Emulator {
+  _MockEmulator(String id) : super(id);
+
+  @override
+  void noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
+}