diff --git a/Tests/Command/CleanCommandTest.php b/Tests/Command/CleanCommandTest.php
index 214495df..ebf3a1a1 100644
--- a/Tests/Command/CleanCommandTest.php
+++ b/Tests/Command/CleanCommandTest.php
@@ -92,9 +92,9 @@ public function testItShouldRemoveExpiredToken(): void
 
         $display = $tester->getDisplay();
 
-        $this->assertContains(sprintf('Removed %d items from %s storage.', $expiredAccessTokens, get_class($this->accessTokenManager)), $display);
-        $this->assertContains(sprintf('Removed %d items from %s storage.', $expiredRefreshTokens, get_class($this->refreshTokenManager)), $display);
-        $this->assertContains(sprintf('Removed %d items from %s storage.', $expiredAuthCodes, get_class($this->authCodeManager)), $display);
+        $this->assertStringContainsString(sprintf('Removed %d items from %s storage.', $expiredAccessTokens, get_class($this->accessTokenManager)), $display);
+        $this->assertStringContainsString(sprintf('Removed %d items from %s storage.', $expiredRefreshTokens, get_class($this->refreshTokenManager)), $display);
+        $this->assertStringContainsString(sprintf('Removed %d items from %s storage.', $expiredAuthCodes, get_class($this->authCodeManager)), $display);
     }
 
     /**
diff --git a/Tests/CustomAssertions.php b/Tests/CustomAssertions.php
new file mode 100644
index 00000000..71f3855e
--- /dev/null
+++ b/Tests/CustomAssertions.php
@@ -0,0 +1,23 @@
+<?php
+
+namespace FOS\OAuthServerBundle\Tests;
+
+use DMS\PHPUnitExtensions\ArraySubset\ArraySubsetAsserts;
+
+trait CustomAssertions {
+    use ArraySubsetAsserts;
+
+    /**
+     * Replacement for assert removed in PHPUnit 9.
+     *
+     * @param mixed $expected
+     * @param object $actualObject
+     */
+    public static function assertAttributeSame($expected, string $actualAttributeName, $actualObject, string $message = ''): void
+    {
+        $prop = new \ReflectionProperty(\get_class($actualObject), $actualAttributeName);
+
+        $prop->setAccessible(true);
+        self::assertSame($expected, $prop->getValue($actualObject));
+    }
+}
diff --git a/Tests/DependencyInjection/ConfigurationTest.php b/Tests/DependencyInjection/ConfigurationTest.php
index 52fb2607..79fc24dd 100644
--- a/Tests/DependencyInjection/ConfigurationTest.php
+++ b/Tests/DependencyInjection/ConfigurationTest.php
@@ -14,12 +14,15 @@
 namespace FOS\OAuthServerBundle\Tests\DependencyInjection;
 
 use FOS\OAuthServerBundle\DependencyInjection\Configuration;
+use FOS\OAuthServerBundle\Tests\CustomAssertions;
 use Symfony\Component\Config\Definition\ConfigurationInterface;
 use Symfony\Component\Config\Definition\Exception\InvalidConfigurationException;
 use Symfony\Component\Config\Definition\Processor;
 
 class ConfigurationTest extends \PHPUnit\Framework\TestCase
 {
+    use CustomAssertions;
+
     public function testShouldImplementConfigurationInterface(): void
     {
         $rc = new \ReflectionClass(Configuration::class);
diff --git a/Tests/Document/AuthCodeManagerTest.php b/Tests/Document/AuthCodeManagerTest.php
index 68c5a6b2..335018c4 100644
--- a/Tests/Document/AuthCodeManagerTest.php
+++ b/Tests/Document/AuthCodeManagerTest.php
@@ -15,10 +15,11 @@
 
 use Doctrine\MongoDB\Query\Builder;
 use Doctrine\ODM\MongoDB\DocumentManager;
-use Doctrine\ODM\MongoDB\DocumentRepository;
+use Doctrine\ODM\MongoDB\Repository\DocumentRepository;
 use Doctrine\ORM\AbstractQuery;
 use FOS\OAuthServerBundle\Document\AuthCodeManager;
 use FOS\OAuthServerBundle\Model\AuthCodeInterface;
+use FOS\OAuthServerBundle\Tests\CustomAssertions;
 
 /**
  * @group time-sensitive
@@ -29,6 +30,8 @@
  */
 class AuthCodeManagerTest extends \PHPUnit\Framework\TestCase
 {
+    use CustomAssertions;
+
     /**
      * @var \PHPUnit\Framework\MockObject\MockObject|DocumentManager
      */
diff --git a/Tests/Document/ClientManagerTest.php b/Tests/Document/ClientManagerTest.php
index 1bf8bcf4..997829bd 100644
--- a/Tests/Document/ClientManagerTest.php
+++ b/Tests/Document/ClientManagerTest.php
@@ -17,6 +17,7 @@
 use Doctrine\ODM\MongoDB\DocumentRepository;
 use FOS\OAuthServerBundle\Document\ClientManager;
 use FOS\OAuthServerBundle\Model\ClientInterface;
+use FOS\OAuthServerBundle\Tests\CustomAssertions;
 
 /**
  * Class ClientManagerTest.
@@ -25,6 +26,8 @@
  */
 class ClientManagerTest extends \PHPUnit\Framework\TestCase
 {
+    use CustomAssertions;
+
     /**
      * @var \PHPUnit\Framework\MockObject\MockObject|DocumentManager
      */
diff --git a/Tests/Entity/AuthCodeManagerTest.php b/Tests/Entity/AuthCodeManagerTest.php
index eedacf70..d5b22f75 100644
--- a/Tests/Entity/AuthCodeManagerTest.php
+++ b/Tests/Entity/AuthCodeManagerTest.php
@@ -20,6 +20,7 @@
 use Doctrine\ORM\QueryBuilder;
 use FOS\OAuthServerBundle\Entity\AuthCodeManager;
 use FOS\OAuthServerBundle\Model\AuthCodeInterface;
+use FOS\OAuthServerBundle\Tests\CustomAssertions;
 
 /**
  * @group time-sensitive
@@ -30,6 +31,8 @@
  */
 class AuthCodeManagerTest extends \PHPUnit\Framework\TestCase
 {
+    use CustomAssertions;
+
     /**
      * @var \PHPUnit\Framework\MockObject\MockObject|EntityManagerInterface
      */
diff --git a/Tests/Entity/ClientManagerTest.php b/Tests/Entity/ClientManagerTest.php
index e4958aa7..e2456be5 100644
--- a/Tests/Entity/ClientManagerTest.php
+++ b/Tests/Entity/ClientManagerTest.php
@@ -17,6 +17,7 @@
 use Doctrine\ORM\EntityRepository;
 use FOS\OAuthServerBundle\Entity\ClientManager;
 use FOS\OAuthServerBundle\Model\ClientInterface;
+use FOS\OAuthServerBundle\Tests\CustomAssertions;
 
 /**
  * Class ClientManagerTest.
@@ -25,6 +26,8 @@
  */
 class ClientManagerTest extends \PHPUnit\Framework\TestCase
 {
+    use CustomAssertions;
+
     /**
      * @var \PHPUnit\Framework\MockObject\MockObject|EntityManagerInterface
      */
diff --git a/Tests/Entity/TokenManagerTest.php b/Tests/Entity/TokenManagerTest.php
index 1cc2d834..d2dc869d 100644
--- a/Tests/Entity/TokenManagerTest.php
+++ b/Tests/Entity/TokenManagerTest.php
@@ -21,6 +21,7 @@
 use FOS\OAuthServerBundle\Entity\AccessToken;
 use FOS\OAuthServerBundle\Entity\TokenManager;
 use FOS\OAuthServerBundle\Model\TokenInterface;
+use FOS\OAuthServerBundle\Tests\CustomAssertions;
 
 /**
  * @group time-sensitive
@@ -31,6 +32,8 @@
  */
 class TokenManagerTest extends \PHPUnit\Framework\TestCase
 {
+    use CustomAssertions;
+
     /**
      * @var \PHPUnit\Framework\MockObject\MockObject|EntityManagerInterface
      */
diff --git a/Tests/Form/Handler/AuthorizeFormHandlerTest.php b/Tests/Form/Handler/AuthorizeFormHandlerTest.php
index dd211252..74d5938d 100644
--- a/Tests/Form/Handler/AuthorizeFormHandlerTest.php
+++ b/Tests/Form/Handler/AuthorizeFormHandlerTest.php
@@ -15,6 +15,7 @@
 
 use FOS\OAuthServerBundle\Form\Handler\AuthorizeFormHandler;
 use FOS\OAuthServerBundle\Form\Model\Authorize;
+use FOS\OAuthServerBundle\Tests\CustomAssertions;
 use Symfony\Bundle\FrameworkBundle\Tests\Fixtures\Serialization\Author;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Symfony\Component\Form\FormInterface;
@@ -29,6 +30,8 @@
  */
 class AuthorizeFormHandlerTest extends \PHPUnit\Framework\TestCase
 {
+    use CustomAssertions;
+
     /**
      * @var FormInterface&\PHPUnit\Framework\MockObject\MockObject
      */
diff --git a/Tests/Functional/config/config.yml b/Tests/Functional/config/config.yml
index ae7bb4f7..6fc71560 100644
--- a/Tests/Functional/config/config.yml
+++ b/Tests/Functional/config/config.yml
@@ -3,6 +3,7 @@ framework:
     secret: test
     router:
         resource: '%kernel.project_dir%/Tests/Functional/config/routing.yml'
+        utf8: true
 
 twig:
     exception_controller: null
diff --git a/composer.json b/composer.json
index f3dc487a..6146f128 100644
--- a/composer.json
+++ b/composer.json
@@ -31,6 +31,7 @@
         "twig/twig": "<1.40 || >=2.0,<2.9"
     },
     "require-dev": {
+        "dms/phpunit-arraysubset-asserts": "^0.1 || ^0.2",
         "doctrine/doctrine-bundle": "^2.0",
         "doctrine/mongodb-odm": "~1.0",
         "doctrine/orm": "~2.2",
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 5192b311..7ea557b2 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -27,4 +27,8 @@
     <listeners>
         <listener class="Symfony\Bridge\PhpUnit\SymfonyTestsListener" />
     </listeners>
+
+    <php>
+        <env name="SYMFONY_DEPRECATIONS_HELPER" value="7" />
+    </php>
 </phpunit>