diff --git a/mdtest/lib/driver_util.dart b/mdtest/lib/driver_util.dart
index ae8ea2d..c53c0b6 100644
--- a/mdtest/lib/driver_util.dart
+++ b/mdtest/lib/driver_util.dart
@@ -1,39 +1,6 @@
 // Copyright 2016 The Vanadium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
+library driver_util;
 
-import 'dart:async';
-import 'dart:io';
-import 'dart:convert' show JSON;
-
-import 'package:flutter_driver/flutter_driver.dart';
-
-import 'src/base/common.dart';
-import 'src/globals.dart';
-
-class DriverUtil {
-  static Future<FlutterDriver> connectByName(String deviceNickname) async {
-    // read the temp spec file to find the device nickname -> observatory port
-    // mapping
-    Directory systemTempDir = Directory.systemTemp;
-    File tempFile = new File('${systemTempDir.path}/$defaultTempSpecsName');
-    // if temp spec file is not found, report error and exit
-    if(!await tempFile.exists()) {
-      printError('Multi-Drive temporary specs file not found.');
-      exit(1);
-    }
-    // decode specs
-    dynamic configs = JSON.decode(await tempFile.readAsString());
-    // report error if nickname is not found
-    if(!configs.containsKey(deviceNickname)) {
-      printError('Device nickname $deviceNickname not found.');
-      exit(1);
-    }
-    // read device id and observatory port
-    String deviceID = configs[deviceNickname]['device-id'];
-    String observatoryUrl = configs[deviceNickname]['observatory-url'];
-    printInfo('$deviceNickname refers to device $deviceID running on url $observatoryUrl');
-    // delegate to flutter driver connect method
-    return await FlutterDriver.connect(dartVmServiceUrl: '$observatoryUrl');
-  }
-}
+export 'src/api/driver_map.dart';
diff --git a/mdtest/lib/src/api/driver_map.dart b/mdtest/lib/src/api/driver_map.dart
new file mode 100644
index 0000000..08e1de0
--- /dev/null
+++ b/mdtest/lib/src/api/driver_map.dart
@@ -0,0 +1,88 @@
+// Copyright 2016 The Vanadium 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 'dart:io';
+import 'dart:convert' show JSON;
+import 'dart:collection';
+
+import 'package:flutter_driver/flutter_driver.dart';
+
+import '../base/common.dart';
+
+/// Singleton pattern is used to load config data only once.
+class Meta {
+  dynamic _config;
+
+  static Meta instance;
+
+  factory Meta() {
+    if (instance == null) {
+      // Read the temp spec file to find the device nickname -> observatory port
+      // mapping.
+      Directory systemTempDir = Directory.systemTemp;
+      File tempFile = new File('${systemTempDir.path}/$defaultTempSpecsName');
+      // if temp spec file is not found, report error and exit.
+      if(!tempFile.existsSync()) {
+        stderr.writeln('mdtest temporary specs file not found.');
+        exit(1);
+      }
+      // Decode specs assuming no exception, because the temp file is
+      // generated by mdtest.
+      dynamic config = JSON.decode(tempFile.readAsStringSync());
+      instance = new Meta._internal(config);
+    }
+    return instance;
+  }
+
+  dynamic get config => instance._config;
+
+  Meta._internal(this._config);
+}
+
+class DriverMap extends UnmodifiableMapBase<String, Future<FlutterDriver>> {
+
+  Meta _meta;
+  Map<String, FlutterDriver> _map;
+
+  DriverMap() {
+    _meta = new Meta();
+    _map = <String, FlutterDriver>{};
+  }
+
+  /// Lazy initializing flutter driver given the nickname.  If the nickname
+  /// does not exist in the test spec, report error and return null.  Otherwise,
+  /// if the flutter driver associated with the nickname is not initialized,
+  /// initialize the driver.  If the flutter driver is initialized, return it.
+  @override
+  Future<FlutterDriver> operator [](String nickname) async {
+    dynamic config = _meta.config;
+    if (config.containsKey(nickname)) {
+      if (!_map.containsKey(nickname)) {
+        String observatoryUrl = config[nickname]['observatory-url'];
+        // Delegate to flutter driver connect method.
+        FlutterDriver driver
+          = await FlutterDriver.connect(dartVmServiceUrl: '$observatoryUrl');
+        _map[nickname] = driver;
+        return driver;
+      }
+      return _map[nickname];
+    }
+    stderr.writeln('Device nickname $nickname not found.');
+    return null;
+  }
+
+  @override
+  Iterable<String> get keys => _meta.config.keys;
+
+  /// Close all connected drivers.
+  void closeAll() {
+    keys.forEach((String nickname) async {
+      FlutterDriver driver = await this[nickname];
+      if (driver != null) {
+        await driver.close();
+      }
+    });
+  }
+}
diff --git a/mdtest/lib/src/base/common.dart b/mdtest/lib/src/base/common.dart
index de1d4d3..a43c389 100644
--- a/mdtest/lib/src/base/common.dart
+++ b/mdtest/lib/src/base/common.dart
@@ -3,4 +3,4 @@
 // license that can be found in the LICENSE file.
 
 const String defaultTempSpecsName = 'tmp.spec';
-const String defaultCodeCoverageDirectoryPath = 'coverage/code_coverage';
+const String defaultCodeCoverageDirectoryPath = 'coverage';
diff --git a/mdtest/lib/src/mobile/device_spec.dart b/mdtest/lib/src/mobile/device_spec.dart
index 77f604f..251eba0 100644
--- a/mdtest/lib/src/mobile/device_spec.dart
+++ b/mdtest/lib/src/mobile/device_spec.dart
@@ -37,6 +37,8 @@
     List<String> checkedProperties = [
       'device-id',
       'model-name',
+      'os-version',
+      'api-level',
       'screen-size'
     ];
     return checkedProperties.every(