diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index b285223..8c38035 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -64,3 +64,24 @@ jobs:
 
             -   name: Run lint
                 run: composer lint
+
+    phpstan:
+        runs-on: ubuntu-latest
+
+        name: PHPStan
+
+        steps:
+            -   name: Checkout code
+                uses: actions/checkout@v4
+
+            -   name: Setup PHP
+                uses: shivammathur/setup-php@v2
+                with:
+                    php-version: 8.5
+                    coverage: none
+
+            -   name: Install Composer dependencies
+                uses: ramsey/composer-install@v3
+
+            -   name: Run phpstan
+                run: composer phpstan
diff --git a/composer.json b/composer.json
index e42e8af..186e544 100644
--- a/composer.json
+++ b/composer.json
@@ -17,7 +17,9 @@
         "illuminate/support": "^9.0 || ^10.0 || ^11.0 || ^12.0",
         "knplabs/gaufrette": "^0.11",
         "phpunit/phpunit": "^9.5",
-        "symfony/validator": "^5.4 || ^6.4 || ^7.0"
+        "symfony/validator": "^5.4 || ^6.4 || ^7.0",
+        "phpstan/phpstan": "^2.1",
+        "phpstan/phpstan-phpunit": "^2.0"
     },
     "suggest": {
         "symfony/validator": "Add validation constraints",
@@ -49,6 +51,9 @@
         ],
         "lint": [
             "php-cs-fixer fix --ansi"
+        ],
+        "phpstan": [
+            "phpstan analyse"
         ]
     }
 }
diff --git a/phpstan.dist.neon b/phpstan.dist.neon
new file mode 100644
index 0000000..30a7c73
--- /dev/null
+++ b/phpstan.dist.neon
@@ -0,0 +1,10 @@
+includes:
+    - vendor/phpstan/phpstan-phpunit/extension.neon
+    - vendor/phpstan/phpstan-phpunit/rules.neon
+    - vendor/phpstan/phpstan/conf/bleedingEdge.neon
+
+parameters:
+    level: 8
+    paths:
+        - src/
+        - tests/
diff --git a/src/EmailChecker/Adapter/AgregatorAdapter.php b/src/EmailChecker/Adapter/AgregatorAdapter.php
index 67e42be..0b893e8 100644
--- a/src/EmailChecker/Adapter/AgregatorAdapter.php
+++ b/src/EmailChecker/Adapter/AgregatorAdapter.php
@@ -18,21 +18,18 @@
  */
 class AgregatorAdapter implements AdapterInterface
 {
+    /**
+     * @var AdapterInterface[]
+     */
     protected $adapters;
 
     /**
-     * Build agregator adapter with a list of adpaters (order matters).
+     * Build aggregator adapter with a list of adapters (order matters).
      *
-     * @param array $adapters List of AdapterInterface objects
+     * @param AdapterInterface[] $adapters List of AdapterInterface objects
      */
     public function __construct(array $adapters)
     {
-        foreach ($adapters as $adapter) {
-            if (!$adapter instanceof AdapterInterface) {
-                throw new \InvalidArgumentException('AgregatorAdapter only accept instances of AdapterInterface');
-            }
-        }
-
         $this->adapters = $adapters;
     }
 
diff --git a/src/EmailChecker/Adapter/ArrayAdapter.php b/src/EmailChecker/Adapter/ArrayAdapter.php
index 4de61fd..56f7513 100644
--- a/src/EmailChecker/Adapter/ArrayAdapter.php
+++ b/src/EmailChecker/Adapter/ArrayAdapter.php
@@ -18,10 +18,13 @@
  */
 class ArrayAdapter implements AdapterInterface
 {
+    /**
+     * @var string[]
+     */
     protected $domains;
 
     /**
-     * @param array $domains List of throwaway domains
+     * @param string[] $domains List of throwaway domains
      */
     public function __construct(array $domains)
     {
diff --git a/src/EmailChecker/Adapter/BuiltInAdapter.php b/src/EmailChecker/Adapter/BuiltInAdapter.php
index e0a5815..0a598cd 100644
--- a/src/EmailChecker/Adapter/BuiltInAdapter.php
+++ b/src/EmailChecker/Adapter/BuiltInAdapter.php
@@ -25,13 +25,19 @@
  */
 class BuiltInAdapter implements AdapterInterface
 {
-    protected $domains;
+    /**
+     * @var string[]|null
+     */
+    protected $domains = null;
 
     public function isThrowawayDomain($domain)
     {
         return in_array($domain, $this->getDomains());
     }
 
+    /**
+     * @return string[]
+     */
     private function getDomains()
     {
         if (null === $this->domains) {
diff --git a/src/EmailChecker/Adapter/FileAdapter.php b/src/EmailChecker/Adapter/FileAdapter.php
index eae9c0c..f1bbeac 100644
--- a/src/EmailChecker/Adapter/FileAdapter.php
+++ b/src/EmailChecker/Adapter/FileAdapter.php
@@ -20,6 +20,9 @@
  */
 class FileAdapter implements AdapterInterface
 {
+    /**
+     * @var string[]
+     */
     protected $domains;
 
     /**
@@ -27,11 +30,12 @@ class FileAdapter implements AdapterInterface
      */
     public function __construct($filename)
     {
-        if (!file_exists($filename)) {
+        $content = file_get_contents($filename);
+        if (false === $content) {
             throw new \InvalidArgumentException(sprintf('File "%s" not found', $filename));
         }
 
-        $this->domains = Utilities::parseLines(file_get_contents($filename));
+        $this->domains = Utilities::parseLines($content);
     }
 
     public function isThrowawayDomain($domain)
diff --git a/src/EmailChecker/Adapter/GaufretteAdapter.php b/src/EmailChecker/Adapter/GaufretteAdapter.php
index 3625b2d..a7a4d21 100644
--- a/src/EmailChecker/Adapter/GaufretteAdapter.php
+++ b/src/EmailChecker/Adapter/GaufretteAdapter.php
@@ -21,6 +21,9 @@
  */
 class GaufretteAdapter implements AdapterInterface
 {
+    /**
+     * @var string[]
+     */
     protected $domains;
 
     public function __construct(File $file)
diff --git a/src/EmailChecker/Constraints/NotThrowawayEmail.php b/src/EmailChecker/Constraints/NotThrowawayEmail.php
index d74c1d1..4a554e6 100644
--- a/src/EmailChecker/Constraints/NotThrowawayEmail.php
+++ b/src/EmailChecker/Constraints/NotThrowawayEmail.php
@@ -21,6 +21,9 @@
 #[\Attribute]
 class NotThrowawayEmail extends Constraint
 {
+    /**
+     * @var string
+     */
     public $message = 'The domain associated with this email is not valid.';
 
     public function __construct(
diff --git a/src/EmailChecker/Constraints/NotThrowawayEmailValidator.php b/src/EmailChecker/Constraints/NotThrowawayEmailValidator.php
index a41d741..50a7f2e 100644
--- a/src/EmailChecker/Constraints/NotThrowawayEmailValidator.php
+++ b/src/EmailChecker/Constraints/NotThrowawayEmailValidator.php
@@ -21,6 +21,9 @@
  */
 class NotThrowawayEmailValidator extends ConstraintValidator
 {
+    /**
+     * @var EmailChecker
+     */
     protected $emailChecker;
 
     public function __construct(?EmailChecker $emailChecker = null)
@@ -28,8 +31,17 @@ public function __construct(?EmailChecker $emailChecker = null)
         $this->emailChecker = $emailChecker ?: new EmailChecker();
     }
 
+    /**
+     * @param mixed $value
+     *
+     * @return void
+     */
     public function validate($value, Constraint $constraint)
     {
+        if (!$constraint instanceof NotThrowawayEmail) {
+            throw new UnexpectedTypeException($constraint, NotThrowawayEmail::class);
+        }
+
         if (null === $value || '' === $value) {
             return;
         }
@@ -38,7 +50,7 @@ public function validate($value, Constraint $constraint)
             throw new UnexpectedTypeException($value, 'string');
         }
 
-        if (!$this->emailChecker->isValid($value)) {
+        if (!$this->emailChecker->isValid((string) $value)) {
             $this->context->addViolation($constraint->message);
         }
     }
diff --git a/src/EmailChecker/EmailChecker.php b/src/EmailChecker/EmailChecker.php
index 510a86e..3acc4df 100644
--- a/src/EmailChecker/EmailChecker.php
+++ b/src/EmailChecker/EmailChecker.php
@@ -22,6 +22,9 @@
  */
 class EmailChecker
 {
+    /**
+     * @var AdapterInterface
+     */
     protected $adapter;
 
     /**
@@ -29,7 +32,7 @@ class EmailChecker
      */
     public function __construct(?AdapterInterface $adapter = null)
     {
-        $this->adapter = $adapter ?: new BuiltInAdapter();
+        $this->adapter = $adapter ?? new BuiltInAdapter();
     }
 
     /**
diff --git a/src/EmailChecker/Laravel/EmailCheckerServiceProvider.php b/src/EmailChecker/Laravel/EmailCheckerServiceProvider.php
index c0732be..c22bf73 100644
--- a/src/EmailChecker/Laravel/EmailCheckerServiceProvider.php
+++ b/src/EmailChecker/Laravel/EmailCheckerServiceProvider.php
@@ -22,10 +22,10 @@
  */
 class EmailCheckerServiceProvider extends ServiceProvider
 {
-    protected $app;
-
     /**
      * Register the factory in the application container.
+     *
+     * @return void
      */
     public function register()
     {
@@ -44,6 +44,8 @@ public function register()
 
     /**
      * Bootstrap any application services.
+     *
+     * @return void
      */
     public function boot(EmailChecker $checker)
     {
@@ -62,7 +64,7 @@ public function boot(EmailChecker $checker)
     /**
      * Get the services provided by the provider.
      *
-     * @return array
+     * @return array<string>
      */
     public function provides()
     {
diff --git a/src/EmailChecker/ThrowawayDomains.php b/src/EmailChecker/ThrowawayDomains.php
index b5e84e0..b7e341a 100644
--- a/src/EmailChecker/ThrowawayDomains.php
+++ b/src/EmailChecker/ThrowawayDomains.php
@@ -15,18 +15,29 @@
  * List of built-in throwaway domains read from the resources folder.
  *
  * @author Matthieu Moquet <matthieu@moquet.net>
+ *
+ * @implements \IteratorAggregate<string>
  */
 class ThrowawayDomains implements \IteratorAggregate, \Countable
 {
+    /**
+     * @var string[]
+     */
     protected $domains;
 
     public function __construct()
     {
-        $this->domains = Utilities::parseLines(file_get_contents(
-            __DIR__.'/../../res/throwaway_domains.txt'
-        ));
+        $content = file_get_contents(__DIR__.'/../../res/throwaway_domains.txt');
+        if (false === $content) {
+            throw new \LogicException('File "throwaway_domains.txt" not found');
+        }
+
+        $this->domains = Utilities::parseLines($content);
     }
 
+    /**
+     * @return string[]
+     */
     public function toArray()
     {
         return $this->domains;
diff --git a/src/EmailChecker/Utilities.php b/src/EmailChecker/Utilities.php
index e73c52d..60d65a4 100644
--- a/src/EmailChecker/Utilities.php
+++ b/src/EmailChecker/Utilities.php
@@ -28,14 +28,10 @@ class Utilities
      *
      * @param string $email The email address to parse
      *
-     * @return array The parts of the email. First the local part, then the domain
+     * @return array{string, string} The parts of the email. First the local part, then the domain
      */
     public static function parseEmailAddress($email)
     {
-        if (!is_string($email)) {
-            throw new InvalidEmailException(sprintf('Expected a string, received %s', gettype($email)));
-        }
-
         $pattern = sprintf('/^(?<local>%s)@(?<domain>%s)$/iD', self::EMAIL_REGEX_LOCAL, self::EMAIL_REGEX_DOMAIN);
 
         if (!preg_match($pattern, $email, $parts)) {
@@ -50,7 +46,7 @@ public static function parseEmailAddress($email)
      *
      * @param string $content The content to parse
      *
-     * @return array Array of cleaned string
+     * @return array<string> Array of cleaned string
      */
     public static function parseLines($content)
     {
@@ -62,10 +58,9 @@ public static function parseLines($content)
         $lines = array_map('strtolower', $lines);
 
         // Remove empty lines and comments
-        $lines = array_filter($lines, function ($line) {
-            return (0 === strlen($line) || '#' === $line[0]) ? false : $line;
-        });
-
-        return $lines;
+        return array_filter(
+            $lines,
+            static fn (string $line): bool => 0 !== strlen($line) && '#' !== $line[0],
+        );
     }
 }
diff --git a/tests/EmailChecker/Tests/Adpater/AgregatorAdapterTest.php b/tests/EmailChecker/Tests/Adpater/AgregatorAdapterTest.php
index 166c758..60bdda1 100644
--- a/tests/EmailChecker/Tests/Adpater/AgregatorAdapterTest.php
+++ b/tests/EmailChecker/Tests/Adpater/AgregatorAdapterTest.php
@@ -15,46 +15,36 @@
 use EmailChecker\Adapter\AgregatorAdapter;
 use EmailChecker\Tests\TestCase;
 
-class AgregatorAdapterTest extends TestCase
+final class AgregatorAdapterTest extends TestCase
 {
-    public function testAllValid()
+    public function testAllValid(): void
     {
         $adapter1 = $this->getAdapterMock(false, 'once');
         $adapter2 = $this->getAdapterMock(false, 'once');
 
-        $this->adapter = new AgregatorAdapter([$adapter1, $adapter2]);
+        $adapter = new AgregatorAdapter([$adapter1, $adapter2]);
 
-        $this->assertFalse($this->adapter->isThrowawayDomain('example.org'));
+        $this->assertFalse($adapter->isThrowawayDomain('example.org'));
     }
 
-    public function testFirstInvalid()
+    public function testFirstInvalid(): void
     {
         $adapter1 = $this->getAdapterMock(true, 'once');
         $adapter2 = $this->getAdapterMock(false, 'never');
 
-        $this->adapter = new AgregatorAdapter([$adapter1, $adapter2]);
+        $adapter = new AgregatorAdapter([$adapter1, $adapter2]);
 
-        $this->assertTrue($this->adapter->isThrowawayDomain('example.org'));
+        $this->assertTrue($adapter->isThrowawayDomain('example.org'));
     }
 
-    public function testSecondInvalid()
+    public function testSecondInvalid(): void
     {
         $adapter1 = $this->getAdapterMock(false, 'once');
         $adapter2 = $this->getAdapterMock(true, 'once');
 
-        $this->adapter = new AgregatorAdapter([$adapter1, $adapter2]);
+        $adapter = new AgregatorAdapter([$adapter1, $adapter2]);
 
-        $this->assertTrue($this->adapter->isThrowawayDomain('example.org'));
-    }
-
-    public function testCheckArrayValuesInstanceOf()
-    {
-        $this->expectException(\InvalidArgumentException::class);
-
-        new AgregatorAdapter([
-            new \stdClass(),
-            new \stdClass(),
-        ]);
+        $this->assertTrue($adapter->isThrowawayDomain('example.org'));
     }
 
     /**
@@ -64,7 +54,7 @@ public function testCheckArrayValuesInstanceOf()
      *
      * @return AdapterInterface The mock adapter
      */
-    protected function getAdapterMock($isThrowawayDomain, $call = 'any')
+    protected function getAdapterMock(bool $isThrowawayDomain, string $call = 'any'): AdapterInterface
     {
         $adapter = $this->createMock(AdapterInterface::class);
         $adapter->expects($this->$call())
diff --git a/tests/EmailChecker/Tests/Adpater/ArrayAdapterTest.php b/tests/EmailChecker/Tests/Adpater/ArrayAdapterTest.php
index 08fe90d..52908a3 100644
--- a/tests/EmailChecker/Tests/Adpater/ArrayAdapterTest.php
+++ b/tests/EmailChecker/Tests/Adpater/ArrayAdapterTest.php
@@ -14,26 +14,26 @@
 use EmailChecker\Adapter\ArrayAdapter;
 use EmailChecker\Tests\TestCase;
 
-class ArrayAdapterTest extends TestCase
+final class ArrayAdapterTest extends TestCase
 {
-    protected static $throawayDomains = [
+    private const DOMAINS = [
         'jetable.org',
         'mailjet.org',
     ];
 
-    protected $adapter;
+    private ArrayAdapter $adapter;
 
     protected function setUp(): void
     {
         parent::setUp();
 
-        $this->adapter = new ArrayAdapter(self::$throawayDomains);
+        $this->adapter = new ArrayAdapter(self::DOMAINS);
     }
 
     /**
      * @dataProvider throwawayDomains
      */
-    public function testThrowawayDomains($domain)
+    public function testThrowawayDomains(string $domain): void
     {
         $this->assertTrue($this->adapter->isThrowawayDomain($domain));
     }
@@ -41,12 +41,12 @@ public function testThrowawayDomains($domain)
     /**
      * @dataProvider notThrowawayDomains
      */
-    public function testNotThrowawayDomains($domain)
+    public function testNotThrowawayDomains(string $domain): void
     {
         $this->assertFalse($this->adapter->isThrowawayDomain($domain));
     }
 
-    public static function throwawayDomains()
+    public static function throwawayDomains(): iterable
     {
         return [
             ['jetable.org'],
@@ -54,7 +54,7 @@ public static function throwawayDomains()
         ];
     }
 
-    public static function notThrowawayDomains()
+    public static function notThrowawayDomains(): iterable
     {
         return [
             ['gmail.com'],
diff --git a/tests/EmailChecker/Tests/Adpater/BuiltInAdapterTest.php b/tests/EmailChecker/Tests/Adpater/BuiltInAdapterTest.php
index 407f9a0..6b9152c 100644
--- a/tests/EmailChecker/Tests/Adpater/BuiltInAdapterTest.php
+++ b/tests/EmailChecker/Tests/Adpater/BuiltInAdapterTest.php
@@ -14,9 +14,9 @@
 use EmailChecker\Adapter\BuiltInAdapter;
 use EmailChecker\Tests\TestCase;
 
-class BuiltInAdapterTest extends TestCase
+final class BuiltInAdapterTest extends TestCase
 {
-    protected $adapter;
+    private BuiltInAdapter $adapter;
 
     protected function setUp(): void
     {
@@ -28,12 +28,12 @@ protected function setUp(): void
     /**
      * @dataProvider throwawayDomains
      */
-    public function testThrowawayDomains($domain)
+    public function testThrowawayDomains(string $domain): void
     {
         $this->assertTrue($this->adapter->isThrowawayDomain($domain));
     }
 
-    public static function throwawayDomains()
+    public static function throwawayDomains(): iterable
     {
         // List of some of the built-in throwaway domains
         return [
diff --git a/tests/EmailChecker/Tests/Adpater/FileAdapterTest.php b/tests/EmailChecker/Tests/Adpater/FileAdapterTest.php
index ab086b4..fa683b3 100644
--- a/tests/EmailChecker/Tests/Adpater/FileAdapterTest.php
+++ b/tests/EmailChecker/Tests/Adpater/FileAdapterTest.php
@@ -14,9 +14,9 @@
 use EmailChecker\Adapter\FileAdapter;
 use EmailChecker\Tests\TestCase;
 
-class FileAdapterTest extends TestCase
+final class FileAdapterTest extends TestCase
 {
-    protected $adapter;
+    private FileAdapter $adapter;
 
     protected function setUp(): void
     {
@@ -28,7 +28,7 @@ protected function setUp(): void
     /**
      * @dataProvider throwawayDomains
      */
-    public function testThrowawayDomains($domain)
+    public function testThrowawayDomains(string $domain): void
     {
         $this->assertTrue($this->adapter->isThrowawayDomain($domain));
     }
@@ -36,12 +36,12 @@ public function testThrowawayDomains($domain)
     /**
      * @dataProvider notThrowawayDomains
      */
-    public function testNotThrowawayDomains($domain)
+    public function testNotThrowawayDomains(string $domain): void
     {
         $this->assertFalse($this->adapter->isThrowawayDomain($domain));
     }
 
-    public static function throwawayDomains()
+    public static function throwawayDomains(): iterable
     {
         return [
             ['jetable.org'],
@@ -51,7 +51,7 @@ public static function throwawayDomains()
         ];
     }
 
-    public static function notThrowawayDomains()
+    public static function notThrowawayDomains(): iterable
     {
         return [
             ['gmail.com'],
diff --git a/tests/EmailChecker/Tests/Adpater/GaufretteAdapterTest.php b/tests/EmailChecker/Tests/Adpater/GaufretteAdapterTest.php
index b3d71a8..13b30eb 100644
--- a/tests/EmailChecker/Tests/Adpater/GaufretteAdapterTest.php
+++ b/tests/EmailChecker/Tests/Adpater/GaufretteAdapterTest.php
@@ -17,9 +17,9 @@
 use Gaufrette\File;
 use Gaufrette\Filesystem;
 
-class GaufretteAdapterTest extends TestCase
+final class GaufretteAdapterTest extends TestCase
 {
-    protected $adapter;
+    private GaufretteAdapter $adapter;
 
     protected function setUp(): void
     {
@@ -34,7 +34,7 @@ protected function setUp(): void
     /**
      * @dataProvider throwawayDomains
      */
-    public function testThrowawayDomains($domain)
+    public function testThrowawayDomains(string $domain): void
     {
         $this->assertTrue($this->adapter->isThrowawayDomain($domain));
     }
@@ -42,12 +42,12 @@ public function testThrowawayDomains($domain)
     /**
      * @dataProvider notThrowawayDomains
      */
-    public function testNotThrowawayDomains($domain)
+    public function testNotThrowawayDomains(string $domain): void
     {
         $this->assertFalse($this->adapter->isThrowawayDomain($domain));
     }
 
-    public static function throwawayDomains()
+    public static function throwawayDomains(): iterable
     {
         return [
             ['jetable.org'],
@@ -57,7 +57,7 @@ public static function throwawayDomains()
         ];
     }
 
-    public static function notThrowawayDomains()
+    public static function notThrowawayDomains(): iterable
     {
         return [
             ['gmail.com'],
diff --git a/tests/EmailChecker/Tests/Constraint/NotThrowawayEmailValidatorTest.php b/tests/EmailChecker/Tests/Constraint/NotThrowawayEmailValidatorTest.php
index ae8ba36..7c33250 100644
--- a/tests/EmailChecker/Tests/Constraint/NotThrowawayEmailValidatorTest.php
+++ b/tests/EmailChecker/Tests/Constraint/NotThrowawayEmailValidatorTest.php
@@ -13,14 +13,16 @@
 
 use EmailChecker\Constraints\NotThrowawayEmail;
 use EmailChecker\Constraints\NotThrowawayEmailValidator;
+use PHPUnit\Framework\MockObject\MockObject;
 use PHPUnit\Framework\TestCase;
 use Symfony\Component\Validator\Context\ExecutionContextInterface;
 use Symfony\Component\Validator\Exception\UnexpectedTypeException;
 
-class NotThrowawayEmailValidatorTest extends TestCase
+final class NotThrowawayEmailValidatorTest extends TestCase
 {
-    protected $context;
-    protected $validator;
+    /** @var ExecutionContextInterface&MockObject */
+    private MockObject $context;
+    private NotThrowawayEmailValidator $validator;
 
     protected function setUp(): void
     {
@@ -31,15 +33,7 @@ protected function setUp(): void
         $this->validator->initialize($this->context);
     }
 
-    protected function tearDown(): void
-    {
-        parent::tearDown();
-
-        $this->context = null;
-        $this->validator = null;
-    }
-
-    public function testNullIsValid()
+    public function testNullIsValid(): void
     {
         $this->context->expects($this->never())
             ->method('addViolation');
@@ -47,7 +41,7 @@ public function testNullIsValid()
         $this->validator->validate(null, new NotThrowawayEmail());
     }
 
-    public function testEmptyStringIsValid()
+    public function testEmptyStringIsValid(): void
     {
         $this->context->expects($this->never())
             ->method('addViolation');
@@ -55,7 +49,7 @@ public function testEmptyStringIsValid()
         $this->validator->validate('', new NotThrowawayEmail());
     }
 
-    public function testExpectsStringCompatibleType()
+    public function testExpectsStringCompatibleType(): void
     {
         $this->expectException(UnexpectedTypeException::class);
 
@@ -65,7 +59,7 @@ public function testExpectsStringCompatibleType()
     /**
      * @dataProvider getValidEmails
      */
-    public function testValidEmails($email)
+    public function testValidEmails(string $email): void
     {
         $this->context->expects($this->never())
             ->method('addViolation');
@@ -73,7 +67,7 @@ public function testValidEmails($email)
         $this->validator->validate($email, new NotThrowawayEmail());
     }
 
-    public function getValidEmails()
+    public function getValidEmails(): iterable
     {
         return [
             ['matthieu@moquet.com'],
@@ -84,7 +78,7 @@ public function getValidEmails()
     /**
      * @dataProvider getInvalidEmails
      */
-    public function testInvalidEmails($email)
+    public function testInvalidEmails(string $email): void
     {
         $constraint = new NotThrowawayEmail([
             'message' => 'myMessage',
@@ -97,7 +91,7 @@ public function testInvalidEmails($email)
         $this->validator->validate($email, $constraint);
     }
 
-    public function getInvalidEmails()
+    public function getInvalidEmails(): iterable
     {
         return [
             // Invalid emails
diff --git a/tests/EmailChecker/Tests/EmailCheckerTest.php b/tests/EmailChecker/Tests/EmailCheckerTest.php
index 1d1d057..f9b3ab1 100644
--- a/tests/EmailChecker/Tests/EmailCheckerTest.php
+++ b/tests/EmailChecker/Tests/EmailCheckerTest.php
@@ -14,33 +14,33 @@
 use EmailChecker\Adapter\AdapterInterface;
 use EmailChecker\EmailChecker;
 
-class EmailCheckerTest extends TestCase
+final class EmailCheckerTest extends TestCase
 {
-    public function testEmailIsValid()
+    public function testEmailIsValid(): void
     {
         $adapter = $this->createMock(AdapterInterface::class);
-        $adapter->expects($this->any())
+        $adapter
              ->method('isThrowawayDomain')
-             ->will($this->returnValue(false));
+             ->willReturn(false);
 
         $checker = new EmailChecker($adapter);
 
         $this->assertTrue($checker->isValid('foo@bar.org'));
     }
 
-    public function testEmailIsNotValid()
+    public function testEmailIsNotValid(): void
     {
         $adapter = $this->createMock(AdapterInterface::class);
-        $adapter->expects($this->any())
+        $adapter
              ->method('isThrowawayDomain')
-             ->will($this->returnValue(true));
+             ->willReturn(true);
 
         $checker = new EmailChecker($adapter);
 
         $this->assertFalse($checker->isValid('foo@bar.org'));
     }
 
-    public function testMalformattedEmail()
+    public function testMalformattedEmail(): void
     {
         $adapter = $this->createMock(AdapterInterface::class);
         $checker = new EmailChecker($adapter);
diff --git a/tests/EmailChecker/Tests/TestCase.php b/tests/EmailChecker/Tests/TestCase.php
index c99275a..3fe6064 100644
--- a/tests/EmailChecker/Tests/TestCase.php
+++ b/tests/EmailChecker/Tests/TestCase.php
@@ -11,10 +11,17 @@
 
 namespace EmailChecker\Tests;
 
-class TestCase extends \PHPUnit\Framework\TestCase
+use PHPUnit\Framework\TestCase as PHPUnitTestCase;
+
+abstract class TestCase extends PHPUnitTestCase
 {
-    protected function getFixtures($file)
+    protected function getFixtures(string $file): string
     {
-        return file_get_contents(__DIR__.'/../../fixtures/'.$file);
+        $content = file_get_contents(__DIR__.'/../../fixtures/'.$file);
+        if (false === $content) {
+            throw new \InvalidArgumentException(sprintf('File "%s" not found', $file));
+        }
+
+        return $content;
     }
 }
diff --git a/tests/EmailChecker/Tests/ThrowawayDomainsTest.php b/tests/EmailChecker/Tests/ThrowawayDomainsTest.php
index 95f14da..12ee8cc 100644
--- a/tests/EmailChecker/Tests/ThrowawayDomainsTest.php
+++ b/tests/EmailChecker/Tests/ThrowawayDomainsTest.php
@@ -13,13 +13,12 @@
 
 use EmailChecker\ThrowawayDomains;
 
-class ThrowawayDomainsTest extends TestCase
+final class ThrowawayDomainsTest extends TestCase
 {
-    public function testIsInstanciable()
+    public function testIsInstanciable(): void
     {
         $domains = new ThrowawayDomains();
 
-        $this->assertTrue(is_array($domains->toArray()));
         $this->assertGreaterThan(0, count($domains));
     }
 }
diff --git a/tests/EmailChecker/Tests/UtilitiesTest.php b/tests/EmailChecker/Tests/UtilitiesTest.php
index 397a90d..331d5be 100644
--- a/tests/EmailChecker/Tests/UtilitiesTest.php
+++ b/tests/EmailChecker/Tests/UtilitiesTest.php
@@ -14,12 +14,12 @@
 use EmailChecker\Exception\InvalidEmailException;
 use EmailChecker\Utilities;
 
-class UtilitiesTest extends TestCase
+final class UtilitiesTest extends TestCase
 {
     /**
      * @dataProvider validEmails
      */
-    public function testParseValidEmail($email, $exceptedLocal, $exceptedDomain)
+    public function testParseValidEmail(string $email, string $exceptedLocal, string $exceptedDomain): void
     {
         list($local, $domain) = Utilities::parseEmailAddress($email);
 
@@ -29,7 +29,7 @@ public function testParseValidEmail($email, $exceptedLocal, $exceptedDomain)
     /**
      * @dataProvider invalidEmails
      */
-    public function testParseInvalidEmail($email)
+    public function testParseInvalidEmail(string $email): void
     {
         try {
             Utilities::parseEmailAddress($email);
@@ -39,7 +39,7 @@ public function testParseInvalidEmail($email)
         }
     }
 
-    public function testParseLines()
+    public function testParseLines(): void
     {
         $content = <<<'TEXT'
 # This is a comment and should be parsed
@@ -68,7 +68,7 @@ public function testParseLines()
         $this->assertEmpty($diffs, sprintf($message, print_r($expectedLines, true), print_r($parsedContent, true)));
     }
 
-    public static function validEmails()
+    public static function validEmails(): iterable
     {
         return [
             ['foo@bar.org', 'foo', 'bar.org'],
@@ -76,7 +76,7 @@ public static function validEmails()
         ];
     }
 
-    public static function invalidEmails()
+    public static function invalidEmails(): iterable
     {
         return [
             ['foo[at]bar.org'],