diff --git a/tests/unit/TestCase.php b/tests/unit/TestCase.php
index dccd3af..d098f30 100644
--- a/tests/unit/TestCase.php
+++ b/tests/unit/TestCase.php
@@ -13,4 +13,23 @@ class TestCase extends \yii\test\TestCase
 		}
 		return isset(self::$params[$name]) ? self::$params[$name] : null;
 	}
+	
+	protected function requireApp($requiredConfig=array())
+	{
+		static $usedConfig = array();
+		static $defaultConfig = array(
+			'id' => 'testapp',
+			'basePath' => __DIR__,
+		);
+		
+		$newConfig = array_merge( $defaultConfig, $requiredConfig );
+		
+		if (!(\yii::$app instanceof \yii\web\Application)) {
+			new \yii\web\Application( $newConfig );
+			$usedConfig = $newConfig;
+		} elseif ($newConfig !== $usedConfig) {
+			new \yii\web\Application( $newConfig );
+			$usedConfig = $newConfig;
+		}
+	}
 }
diff --git a/tests/unit/framework/caching/CacheTest.php b/tests/unit/framework/caching/CacheTest.php
index f9db4f4..f3eda7a 100644
--- a/tests/unit/framework/caching/CacheTest.php
+++ b/tests/unit/framework/caching/CacheTest.php
@@ -13,6 +13,12 @@ abstract class CacheTest extends TestCase
 	 */
 	abstract protected function getCacheInstance();
 
+	protected function setUp()
+	{
+		parent::setUp();
+		$this->requireApp();
+	}
+	
 	public function testSet()
 	{
 		$cache = $this->getCacheInstance();
diff --git a/tests/unit/framework/caching/DbCacheTest.php b/tests/unit/framework/caching/DbCacheTest.php
index a41667c..a68a278 100644
--- a/tests/unit/framework/caching/DbCacheTest.php
+++ b/tests/unit/framework/caching/DbCacheTest.php
@@ -17,6 +17,8 @@ class DbCacheTest extends CacheTest
 			$this->markTestSkipped('pdo and pdo_mysql extensions are required.');
 		}
 
+		parent::setUp();
+		
 		$this->getConnection()->createCommand("
 			CREATE TABLE IF NOT EXISTS tbl_cache (
 				id char(128) NOT NULL,
diff --git a/tests/unit/framework/helpers/HtmlTest.php b/tests/unit/framework/helpers/HtmlTest.php
index 6011594..9ba6b43 100644
--- a/tests/unit/framework/helpers/HtmlTest.php
+++ b/tests/unit/framework/helpers/HtmlTest.php
@@ -4,15 +4,13 @@ namespace yiiunit\framework\helpers;
 
 use Yii;
 use yii\helpers\Html;
-use yii\web\Application;
+use yiiunit\TestCase;
 
-class HtmlTest extends \yii\test\TestCase
+class HtmlTest extends TestCase
 {
 	public function setUp()
 	{
-		new Application(array(
-			'id' => 'test',
-			'basePath' => '@yiiunit/runtime',
+		$this->requireApp(array(
 			'components' => array(
 				'request' => array(
 					'class' => 'yii\web\Request',
@@ -30,11 +28,6 @@ class HtmlTest extends \yii\test\TestCase
 		$this->assertEquals($expected, $actual);
 	}
 
-	public function tearDown()
-	{
-		Yii::$app = null;
-	}
-
 	public function testEncode()
 	{
 		$this->assertEquals("a&lt;&gt;&amp;&quot;&#039;", Html::encode("a<>&\"'"));