diff --git a/composer.json b/composer.json
index 1774d16..9b9e569 100644
--- a/composer.json
+++ b/composer.json
@@ -32,7 +32,7 @@
     },
     "require-dev": {
         "yiisoft/yii2-coding-standards": "~2.0",
-        "phpunit/phpunit": "^7.5.20"
+        "phpunit/phpunit": "^6.5.14"
     },
     "repositories": [
         {
diff --git a/tests/PopoverTest.php b/tests/PopoverTest.php
index cba1fa7..1dc05b1 100644
--- a/tests/PopoverTest.php
+++ b/tests/PopoverTest.php
@@ -2,6 +2,7 @@
 
 namespace yiiunit\extensions\bootstrap5;
 
+use PHPUnit\Framework\Constraint\IsType;
 use Yii;
 use yii\bootstrap5\Html;
 use yii\bootstrap5\Popover;
@@ -35,7 +36,7 @@ HTML;
 
         $js = Yii::$app->view->js[View::POS_READY];
 
-        $this->assertIsArray($js);
+        $this->assertInternalType(IsType::TYPE_ARRAY, $js);
         $options = array_shift($js);
 
         $this->assertContainsWithoutLE("jQuery('#w0').popover({", $options);
@@ -54,7 +55,7 @@ HTML;
 
         $js = Yii::$app->view->js[View::POS_READY];
 
-        $this->assertIsArray($js);
+        $this->assertInternalType(IsType::TYPE_ARRAY, $js);
         $options = array_shift($js);
 
         $this->assertContainsWithoutLE('"content":"\u003Cspan class=\u0022test-content\u0022\u003ETest content\u003C\/span\u003E"', $options);