diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 988beb6b..dbe953f8 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -14,18 +14,36 @@ jobs:
       matrix:
         include:
           - php: '7.4'
+            symfony-require: 4.4.*
           - php: '8.0'
+            symfony-require: 5.3.*
+          - php: '8.0'
+            symfony-require: 6.0.*
+            stability: dev
           - php: '8.1'
-            mode: experimental
+      fail-fast: false
 
     steps:
       - name: Checkout
         uses: actions/checkout@v2
 
-      - name: "Install dependencies with Composer"
-        uses: "ramsey/composer-install@v1"
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
         with:
-          composer-options: "--prefer-dist"
+          php-version: "${{ matrix.php }}"
+          coverage: none
+
+      - name: Configure Composer minimum stability
+        if: matrix.stability
+        run: composer config minimum-stability ${{ matrix.stability }}
+
+      - name: Install symfony/flex
+        run: composer global require symfony/flex
+
+      - name: Install dependencies
+        env:
+          SYMFONY_REQUIRE: "${{ matrix.symfony-require }}"
+        run: composer update --prefer-dist
 
       - name: "Run PHPUnit"
         run: "vendor/bin/phpunit"
diff --git a/composer.json b/composer.json
index 53ddbada..00f12867 100644
--- a/composer.json
+++ b/composer.json
@@ -14,17 +14,18 @@
     "require": {
         "php": ">=7.4",
         "giggsey/libphonenumber-for-php": "^8.0",
-        "symfony/framework-bundle": "^4.4|^5.3",
-        "symfony/intl": "^4.4|^5.3"
+        "symfony/framework-bundle": "^4.4|^5.3|^6.0",
+        "symfony/intl": "^4.4|^5.3|^6.0"
     },
     "require-dev": {
         "doctrine/doctrine-bundle": "^1.12|^2.0",
-        "phpunit/phpunit": "^8.4",
-        "symfony/form": "^4.4|^5.3",
-        "symfony/property-access": "^4.4|^5.3",
-        "symfony/serializer": "^4.4|^5.3",
-        "symfony/twig-bundle": "^4.4|^5.3",
-        "symfony/validator": "^4.4|^5.3"
+        "phpspec/prophecy-phpunit": "^2.0",
+        "phpunit/phpunit": "^9.5",
+        "symfony/form": "^4.4|^5.3|^6.0",
+        "symfony/property-access": "^4.4|^5.3|^6.0",
+        "symfony/serializer": "^4.4|^5.3|^6.0.1",
+        "symfony/twig-bundle": "^4.4|^5.3|^6.0",
+        "symfony/validator": "^4.4|^5.3|^6.0"
     },
     "suggest": {
         "doctrine/doctrine-bundle": "Add a DBAL mapping type",
@@ -51,5 +52,8 @@
         "branch-alias": {
             "dev-master": "3.5.x-dev"
         }
+    },
+    "conflict": {
+        "symfony/serializer": "6.0.0"
     }
 }
diff --git a/src/Twig/Extension/PhoneNumberHelperExtension.php b/src/Twig/Extension/PhoneNumberHelperExtension.php
index 71bbbf44..bb7f6e3a 100644
--- a/src/Twig/Extension/PhoneNumberHelperExtension.php
+++ b/src/Twig/Extension/PhoneNumberHelperExtension.php
@@ -41,6 +41,8 @@ public function __construct(PhoneNumberHelper $helper)
 
     /**
      * {@inheritdoc}
+     *
+     * @return array
      */
     public function getFunctions()
     {
@@ -53,6 +55,8 @@ public function getFunctions()
 
     /**
      * {@inheritdoc}
+     *
+     * @return array
      */
     public function getFilters()
     {
@@ -64,6 +68,8 @@ public function getFilters()
 
     /**
      * {@inheritdoc}
+     *
+     * @return array
      */
     public function getTests()
     {
diff --git a/tests/Doctrine/DBAL/Types/PhoneNumberTypeTest.php b/tests/Doctrine/DBAL/Types/PhoneNumberTypeTest.php
index d6c5fbe2..ba5e64ed 100644
--- a/tests/Doctrine/DBAL/Types/PhoneNumberTypeTest.php
+++ b/tests/Doctrine/DBAL/Types/PhoneNumberTypeTest.php
@@ -18,12 +18,15 @@
 use libphonenumber\PhoneNumberUtil;
 use Misd\PhoneNumberBundle\Doctrine\DBAL\Types\PhoneNumberType;
 use PHPUnit\Framework\TestCase;
+use Prophecy\PhpUnit\ProphecyTrait;
 
 /**
  * Phone number type test.
  */
 class PhoneNumberTypeTest extends TestCase
 {
+    use ProphecyTrait;
+
     /**
      * @var AbstractPlatform
      */
diff --git a/tests/Serializer/Normalizer/PhoneNumberNormalizerTest.php b/tests/Serializer/Normalizer/PhoneNumberNormalizerTest.php
index 36626ace..20abdebe 100644
--- a/tests/Serializer/Normalizer/PhoneNumberNormalizerTest.php
+++ b/tests/Serializer/Normalizer/PhoneNumberNormalizerTest.php
@@ -18,6 +18,7 @@
 use Misd\PhoneNumberBundle\Serializer\Normalizer\PhoneNumberNormalizer;
 use PHPUnit\Framework\TestCase;
 use Prophecy\Argument;
+use Prophecy\PhpUnit\ProphecyTrait;
 use Symfony\Component\Serializer\Exception\UnexpectedValueException;
 use Symfony\Component\Serializer\Serializer;
 
@@ -26,6 +27,8 @@
  */
 class PhoneNumberNormalizerTest extends TestCase
 {
+    use ProphecyTrait;
+
     protected function setUp(): void
     {
         if (!class_exists(Serializer::class)) {
diff --git a/tests/Templating/Helper/PhoneNumberHelperTest.php b/tests/Templating/Helper/PhoneNumberHelperTest.php
index 7a923cad..4a97b986 100644
--- a/tests/Templating/Helper/PhoneNumberHelperTest.php
+++ b/tests/Templating/Helper/PhoneNumberHelperTest.php
@@ -17,12 +17,15 @@
 use Misd\PhoneNumberBundle\Exception\InvalidArgumentException;
 use Misd\PhoneNumberBundle\Templating\Helper\PhoneNumberHelper;
 use PHPUnit\Framework\TestCase;
+use Prophecy\PhpUnit\ProphecyTrait;
 
 /**
  * Phone number templating helper test.
  */
 class PhoneNumberHelperTest extends TestCase
 {
+    use ProphecyTrait;
+
     protected $phoneNumberUtil;
     protected $helper;
 
diff --git a/tests/Validator/Constraints/PhoneNumberValidatorTest.php b/tests/Validator/Constraints/PhoneNumberValidatorTest.php
index 654555f2..d417455d 100644
--- a/tests/Validator/Constraints/PhoneNumberValidatorTest.php
+++ b/tests/Validator/Constraints/PhoneNumberValidatorTest.php
@@ -14,8 +14,8 @@
 use libphonenumber\PhoneNumberUtil;
 use Misd\PhoneNumberBundle\Validator\Constraints\PhoneNumber;
 use Misd\PhoneNumberBundle\Validator\Constraints\PhoneNumberValidator;
+use PHPUnit\Framework\MockObject\MockObject;
 use PHPUnit\Framework\TestCase;
-use Prophecy\Argument;
 use Symfony\Component\Validator\Context\ExecutionContextInterface;
 use Symfony\Component\Validator\Exception\UnexpectedTypeException;
 use Symfony\Component\Validator\Mapping\ClassMetadata;
@@ -28,7 +28,7 @@
 class PhoneNumberValidatorTest extends TestCase
 {
     /**
-     * @var \Symfony\Component\Validator\Context\ExecutionContextInterface|\PHPUnit_Framework_MockObject_MockObject
+     * @var \Symfony\Component\Validator\Context\ExecutionContextInterface|MockObject
      */
     protected $context;
 
@@ -39,12 +39,12 @@ class PhoneNumberValidatorTest extends TestCase
 
     protected function setUp(): void
     {
-        $this->context = $this->prophesize(ExecutionContextInterface::class);
+        $this->context = $this->createMock(ExecutionContextInterface::class);
 
         $this->validator = new PhoneNumberValidator(PhoneNumberUtil::getInstance());
-        $this->validator->initialize($this->context->reveal());
+        $this->validator->initialize($this->context);
 
-        $this->context->getObject()->willReturn(new Foo());
+        $this->context->method('getObject')->willReturn(new Foo());
     }
 
     /**
@@ -67,14 +67,28 @@ public function testValidate($value, $violates, $type = null, $defaultRegion = n
         }
 
         if (true === $violates) {
-            $constraintViolationBuilder = $this->prophesize(ConstraintViolationBuilderInterface::class);
-            $constraintViolationBuilder->setParameter(Argument::type('string'), Argument::type('string'))->willReturn($constraintViolationBuilder->reveal());
-            $constraintViolationBuilder->setCode(Argument::type('string'))->willReturn($constraintViolationBuilder->reveal());
-            $constraintViolationBuilder->addViolation()->willReturn($constraintViolationBuilder->reveal());
-
-            $this->context->buildViolation($constraint->getMessage())->shouldBeCalledTimes(1)->willReturn($constraintViolationBuilder->reveal());
+            $constraintViolationBuilder = $this->createMock(ConstraintViolationBuilderInterface::class);
+            $constraintViolationBuilder
+                ->expects($this->exactly(2))
+                ->method('setParameter')
+                ->with($this->isType('string'), $this->isType('string'))
+                ->willReturn($constraintViolationBuilder);
+            $constraintViolationBuilder
+                ->expects($this->once())
+                ->method('setCode')
+                ->with($this->isType('string'))
+                ->willReturn($constraintViolationBuilder);
+            $constraintViolationBuilder
+                ->method('addViolation')
+                ->willReturn($constraintViolationBuilder);
+
+            $this->context
+                ->expects($this->once())
+                ->method('buildViolation')
+                ->with($constraint->getMessage())
+                ->willReturn($constraintViolationBuilder);
         } else {
-            $this->context->buildViolation()->shouldNotBeCalled();
+            $this->context->expects($this->never())->method('buildViolation');
         }
 
         $this->validator->validate($value, $constraint);