diff --git a/apps/basic/config/web.php b/apps/basic/config/web.php
index d576599..16bc5a1 100644
--- a/apps/basic/config/web.php
+++ b/apps/basic/config/web.php
@@ -7,7 +7,7 @@ return array(
 	'modules' => array(
 		'debug' => array(
 			'class' => 'yii\debug\Module',
-			'enabled' => YII_DEBUG && YII_ENV === 'dev',
+			'enabled' => YII_DEBUG && YII_ENV_DEV,
 		),
 	),
 	'components' => array(
diff --git a/apps/basic/controllers/SiteController.php b/apps/basic/controllers/SiteController.php
index 9df4819..b2eec12 100644
--- a/apps/basic/controllers/SiteController.php
+++ b/apps/basic/controllers/SiteController.php
@@ -14,7 +14,7 @@ class SiteController extends Controller
 		return array(
 			'captcha' => array(
 				'class' => 'yii\web\CaptchaAction',
-				'fixedVerifyCode' => YII_ENV === 'test' ? 'testme' : null,
+				'fixedVerifyCode' => YII_ENV_DEV ? 'testme' : null,
 			),
 		);
 	}
diff --git a/framework/yii/YiiBase.php b/framework/yii/YiiBase.php
index 25573b7..2f03bba 100644
--- a/framework/yii/YiiBase.php
+++ b/framework/yii/YiiBase.php
@@ -17,6 +17,10 @@ use yii\log\Logger;
  */
 defined('YII_BEGIN_TIME') or define('YII_BEGIN_TIME', microtime(true));
 /**
+ * This constant defines the framework installation directory.
+ */
+defined('YII_PATH') or define('YII_PATH', __DIR__);
+/**
  * This constant defines whether the application should be in debug mode or not. Defaults to false.
  */
 defined('YII_DEBUG') or define('YII_DEBUG', false);
@@ -26,9 +30,18 @@ defined('YII_DEBUG') or define('YII_DEBUG', false);
  */
 defined('YII_ENV') or define('YII_ENV', 'prod');
 /**
- * This constant defines the framework installation directory.
+ * Whether the the application is running in production environment
  */
-defined('YII_PATH') or define('YII_PATH', __DIR__);
+defined('YII_ENV_PROD') or define('YII_ENV_PROD', YII_ENV === 'prod');
+/**
+ * Whether the the application is running in development environment
+ */
+defined('YII_ENV_DEV') or define('YII_ENV_DEV', YII_ENV === 'dev');
+/**
+ * Whether the the application is running in testing environment
+ */
+defined('YII_ENV_TEST') or define('YII_ENV_TEST', YII_ENV === 'test');
+
 /**
  * This constant defines whether error handling should be enabled. Defaults to true.
  */
diff --git a/framework/yii/base/ErrorHandler.php b/framework/yii/base/ErrorHandler.php
index 42ebb18..39c87b0 100644
--- a/framework/yii/base/ErrorHandler.php
+++ b/framework/yii/base/ErrorHandler.php
@@ -82,7 +82,7 @@ class ErrorHandler extends Component
 	 */
 	protected function renderException($exception)
 	{
-		if (Yii::$app instanceof \yii\console\Application || YII_ENV === 'test') {
+		if (Yii::$app instanceof \yii\console\Application || YII_ENV_TEST) {
 			echo Yii::$app->renderException($exception);
 			return;
 		}
diff --git a/framework/yii/data/IDataProvider.php b/framework/yii/data/IDataProvider.php
index 024be90..7b6dc93 100644
--- a/framework/yii/data/IDataProvider.php
+++ b/framework/yii/data/IDataProvider.php
@@ -10,9 +10,8 @@ namespace yii\data;
 /**
  * IDataProvider is the interface that must be implemented by data provider classes.
  *
- * Data providers are components that can provide data that are sorted and paginated.
- * Data providers are often used with widgets, such as [[GridView]], [[ListView]]
- * that display data and support sorting and pagination.
+ * Data providers are components that sort and paginate data, and provide them to widgets
+ * such as [[GridView]], [[ListView]].
  *
  * @author Qiang Xue <qiang.xue@gmail.com>
  * @since 2.0
diff --git a/framework/yii/log/Logger.php b/framework/yii/log/Logger.php
index 540c832..bb7cea5 100644
--- a/framework/yii/log/Logger.php
+++ b/framework/yii/log/Logger.php
@@ -150,7 +150,7 @@ class Logger extends Component
 	{
 		parent::init();
 		if ($this->traceLevel === null) {
-			$this->traceLevel = YII_ENV === 'dev' ? 3 : 0;
+			$this->traceLevel = YII_ENV_DEV ? 3 : 0;
 		}
 		foreach ($this->targets as $name => $target) {
 			if (!$target instanceof Target) {
diff --git a/framework/yii/web/User.php b/framework/yii/web/User.php
index 54831ba..e202e8e 100644
--- a/framework/yii/web/User.php
+++ b/framework/yii/web/User.php
@@ -416,7 +416,7 @@ class User extends Component
 	public function switchIdentity($identity, $duration = 0)
 	{
 		$session = Yii::$app->getSession();
-		if (YII_ENV !== 'test') {
+		if (!YII_ENV_TEST) {
 			$session->regenerateID(true);
 		}
 		$this->setIdentity($identity);