diff --git a/src/Symfony/Component/ErrorRenderer/Tests/Exception/FlattenExceptionTest.php b/src/Symfony/Component/ErrorRenderer/Tests/Exception/FlattenExceptionTest.php
index 0420469891..ca022209f2 100644
--- a/src/Symfony/Component/ErrorRenderer/Tests/Exception/FlattenExceptionTest.php
+++ b/src/Symfony/Component/ErrorRenderer/Tests/Exception/FlattenExceptionTest.php
@@ -305,7 +305,7 @@ class FlattenExceptionTest extends TestCase
 
         $flattened = FlattenException::createFromThrowable($exception);
         $trace = $flattened->getTrace();
-        $this->assertContains('*DEEP NESTED ARRAY*', serialize($trace));
+        $this->assertStringContainsString('*DEEP NESTED ARRAY*', serialize($trace));
     }
 
     public function testTooBigArray()
@@ -329,8 +329,8 @@ class FlattenExceptionTest extends TestCase
 
         $serializeTrace = serialize($trace);
 
-        $this->assertContains('*SKIPPED over 10000 entries*', $serializeTrace);
-        $this->assertNotContains('*value1*', $serializeTrace);
+        $this->assertStringContainsString('*SKIPPED over 10000 entries*', $serializeTrace);
+        $this->assertStringNotContainsString('*value1*', $serializeTrace);
     }
 
     public function testAnonymousClass()
diff --git a/src/Symfony/Component/Mime/Tests/Crypto/SMimeTestCase.php b/src/Symfony/Component/Mime/Tests/Crypto/SMimeTestCase.php
index f562f187f2..0bd3c139c4 100644
--- a/src/Symfony/Component/Mime/Tests/Crypto/SMimeTestCase.php
+++ b/src/Symfony/Component/Mime/Tests/Crypto/SMimeTestCase.php
@@ -55,7 +55,7 @@ abstract class SMimeTestCase extends TestCase
     protected function assertMessageHeaders(Message $message, RawMessage $originalMessage): void
     {
         $messageString = $message->toString();
-        self::assertNotContains('Bcc: ', $messageString, '', true);
+        self::assertStringNotContainsString('Bcc: ', $messageString, '', true);
 
         if (!$originalMessage instanceof Message) {
             return;
@@ -67,7 +67,7 @@ abstract class SMimeTestCase extends TestCase
 
         if ($originalMessage->getHeaders()->has('Subject')) {
             self::assertEquals($originalMessage->getHeaders()->get('Subject'), $message->getPreparedHeaders()->get('Subject'));
-            self::assertContains('Subject:', $messageString, '', true);
+            self::assertStringContainsString('Subject:', $messageString, '', true);
         }
     }
 }