diff --git a/composer.json b/composer.json
index 6db31bc..5e48e3c 100644
--- a/composer.json
+++ b/composer.json
@@ -13,8 +13,9 @@
     "homepage": "https://github.com/Maks3w/SwaggerAssertions",
     "require": {
         "php": ">= 7.1",
+        "ext-json": "*",
         "justinrainbow/json-schema": "^5",
-        "phpunit/phpunit": "^6.0||^7.0",
+        "phpunit/phpunit": "^7.5||^8.0",
         "rize/uri-template": "^0.3.0",
         "zendframework/zend-http": "2.5 - 3"
     },
diff --git a/examples/PhpUnit/AssertTest.php b/examples/PhpUnit/AssertTest.php
index ceec2af..80e1173 100644
--- a/examples/PhpUnit/AssertTest.php
+++ b/examples/PhpUnit/AssertTest.php
@@ -26,17 +26,17 @@ class AssertTest extends TestCase
      */
     protected $guzzleHttpClient;
 
-    public static function setUpBeforeClass()
+    public static function setUpBeforeClass(): void
     {
         self::$schemaManager = SchemaManager::fromUri('http://petstore.swagger.io/v2/swagger.json');
     }
 
-    protected function setUp()
+    protected function setUp(): void
     {
         $this->guzzleHttpClient = new Client(['headers' => ['User-Agent' => 'https://github.com/Maks3w/SwaggerAssertions']]);
     }
 
-    public function testFetchPetBodyMatchDefinition()
+    public function testFetchPetBodyMatchDefinition(): void
     {
         $request = new Request('GET', 'http://petstore.swagger.io/v2/pet/findByStatus');
         $request = $request->withHeader('Accept', 'application/json');
@@ -45,6 +45,6 @@ public function testFetchPetBodyMatchDefinition()
 
         $responseBody = json_decode((string) $response->getBody());
 
-        $this->assertResponseBodyMatch($responseBody, self::$schemaManager, '/v2/pet/findByStatus', 'get', 200);
+        self::assertResponseBodyMatch($responseBody, self::$schemaManager, '/v2/pet/findByStatus', 'get', 200);
     }
 }
diff --git a/examples/PhpUnit/LocalFileTest.php b/examples/PhpUnit/LocalFileTest.php
index de21a79..946644a 100644
--- a/examples/PhpUnit/LocalFileTest.php
+++ b/examples/PhpUnit/LocalFileTest.php
@@ -26,7 +26,7 @@ class LocalFileTest extends TestCase
      */
     protected $guzzleHttpClient;
 
-    public static function setUpBeforeClass()
+    public static function setUpBeforeClass(): void
     {
         $filePath = __DIR__ . '/../fixtures/pet_store.json';
 
@@ -34,12 +34,12 @@ public static function setUpBeforeClass()
         self::$schemaManager = new SchemaManager(json_decode(file_get_contents($filePath)));
     }
 
-    protected function setUp()
+    protected function setUp(): void
     {
         $this->guzzleHttpClient = new Client(['headers' => ['User-Agent' => 'https://github.com/Maks3w/SwaggerAssertions']]);
     }
 
-    public function testFetchPetBodyMatchDefinition()
+    public function testFetchPetBodyMatchDefinition(): void
     {
         $request = new Request('GET', 'http://petstore.swagger.io/v2/pet/findByStatus');
         $request = $request->withHeader('Accept', 'application/json');
@@ -48,6 +48,6 @@ public function testFetchPetBodyMatchDefinition()
 
         $responseBody = json_decode((string) $response->getBody());
 
-        $this->assertResponseBodyMatch($responseBody, self::$schemaManager, '/v2/pet/findByStatus', 'get', 200);
+        self::assertResponseBodyMatch($responseBody, self::$schemaManager, '/v2/pet/findByStatus', 'get', 200);
     }
 }
diff --git a/examples/PhpUnit/Psr7WithGuzzleV6Test.php b/examples/PhpUnit/Psr7WithGuzzleV6Test.php
index 1c5a7e4..36307fb 100644
--- a/examples/PhpUnit/Psr7WithGuzzleV6Test.php
+++ b/examples/PhpUnit/Psr7WithGuzzleV6Test.php
@@ -26,33 +26,33 @@ class Psr7WithGuzzleV6Test extends TestCase
      */
     protected $guzzleHttpClient;
 
-    public static function setUpBeforeClass()
+    public static function setUpBeforeClass(): void
     {
         self::$schemaManager = SchemaManager::fromUri('http://petstore.swagger.io/v2/swagger.json');
     }
 
-    protected function setUp()
+    protected function setUp(): void
     {
         $this->guzzleHttpClient = new Client(['headers' => ['User-Agent' => 'https://github.com/Maks3w/SwaggerAssertions']]);
     }
 
-    public function testFetchPetMatchDefinition()
+    public function testFetchPetMatchDefinition(): void
     {
         $request = new Request('GET', 'http://petstore.swagger.io/v2/store/inventory');
         $request = $request->withHeader('Accept', 'application/json');
 
         $response = $this->guzzleHttpClient->send($request);
 
-        $this->assertResponseAndRequestMatch($response, $request, self::$schemaManager);
+        self::assertResponseAndRequestMatch($response, $request, self::$schemaManager);
     }
 
-    public function testOnlyResponse()
+    public function testOnlyResponse(): void
     {
         $request = new Request('GET', 'http://petstore.swagger.io/v2/pet/findByStatus');
         $request = $request->withHeader('Accept', 'application/json');
 
         $response = $this->guzzleHttpClient->send($request);
 
-        $this->assertResponseMatch($response, self::$schemaManager, '/v2/pet/findByStatus', 'get');
+        self::assertResponseMatch($response, self::$schemaManager, '/v2/pet/findByStatus', 'get');
     }
 }
diff --git a/src/PhpUnit/AssertsTrait.php b/src/PhpUnit/AssertsTrait.php
index 7dab9a2..f8d4147 100644
--- a/src/PhpUnit/AssertsTrait.php
+++ b/src/PhpUnit/AssertsTrait.php
@@ -7,7 +7,6 @@
 use FR3D\SwaggerAssertions\SchemaManager;
 use JsonSchema\Validator;
 use PHPUnit\Framework\Assert;
-use stdClass;
 use Zend\Http\Header\ContentType;
 
 /**
@@ -18,23 +17,23 @@ trait AssertsTrait
     /**
      * Asserts response body match with the response schema.
      *
-     * @param stdClass|stdClass[] $responseBody
+     * @param mixed $responseBody
      * @param string $path percent-encoded path used on the request.
      */
-    public function assertResponseBodyMatch(
+    public static function assertResponseBodyMatch(
         $responseBody,
         SchemaManager $schemaManager,
         string $path,
         string $httpMethod,
         int $httpCode,
         string $message = ''
-    ) {
+    ): void {
         if (!$schemaManager->findPathInTemplates($path, $template, $params)) {
             throw new \RuntimeException('Request URI does not match with any swagger path definition');
         }
 
         $bodySchema = $schemaManager->getResponseSchema($template, $httpMethod, (string) $httpCode);
-        $constraint = new JsonSchemaConstraint($bodySchema, 'response body', $this->getValidator());
+        $constraint = new JsonSchemaConstraint($bodySchema, 'response body', self::getValidator());
 
         Assert::assertThat($responseBody, $constraint, $message);
     }
@@ -42,22 +41,22 @@ public function assertResponseBodyMatch(
     /**
      * Asserts request body match with the request schema.
      *
-     * @param stdClass|stdClass[] $requestBody
+     * @param mixed $requestBody
      * @param string $path percent-encoded path used on the request.
      */
-    public function assertRequestBodyMatch(
+    public static function assertRequestBodyMatch(
         $requestBody,
         SchemaManager $schemaManager,
         string $path,
         string $httpMethod,
         string $message = ''
-    ) {
+    ): void {
         if (!$schemaManager->findPathInTemplates($path, $template, $params)) {
             throw new \RuntimeException('Request URI does not match with any swagger path definition');
         }
 
         $bodySchema = $schemaManager->getRequestSchema($template, $httpMethod);
-        $constraint = new JsonSchemaConstraint($bodySchema, 'request body', $this->getValidator());
+        $constraint = new JsonSchemaConstraint($bodySchema, 'request body', self::getValidator());
 
         Assert::assertThat($requestBody, $constraint, $message);
     }
@@ -67,13 +66,13 @@ public function assertRequestBodyMatch(
      *
      * @param string $path percent-encoded path used on the request.
      */
-    public function assertResponseMediaTypeMatch(
+    public static function assertResponseMediaTypeMatch(
         string $responseMediaType,
         SchemaManager $schemaManager,
         string $path,
         string $httpMethod,
         string $message = ''
-    ) {
+    ): void {
         if (!$schemaManager->findPathInTemplates($path, $template, $params)) {
             // @codeCoverageIgnoreStart
             throw new \RuntimeException('Request URI does not match with any swagger path definition');
@@ -94,13 +93,13 @@ public function assertResponseMediaTypeMatch(
      *
      * @param string $path percent-encoded path used on the request.
      */
-    public function assertRequestMediaTypeMatch(
+    public static function assertRequestMediaTypeMatch(
         string $requestMediaType,
         SchemaManager $schemaManager,
         string $path,
         string $httpMethod,
         string $message = ''
-    ) {
+    ): void {
         if (!$schemaManager->findPathInTemplates($path, $template, $params)) {
             // @codeCoverageIgnoreStart
             throw new \RuntimeException('Request URI does not match with any swagger path definition');
@@ -122,14 +121,14 @@ public function assertRequestMediaTypeMatch(
      * @param string[] $headers
      * @param string $path percent-encoded path used on the request.
      */
-    public function assertResponseHeadersMatch(
+    public static function assertResponseHeadersMatch(
         array $headers,
         SchemaManager $schemaManager,
         string $path,
         string $httpMethod,
         int $httpCode,
         string $message = ''
-    ) {
+    ): void {
         if (!$schemaManager->findPathInTemplates($path, $template, $params)) {
             // @codeCoverageIgnoreStart
             throw new \RuntimeException('Request URI does not match with any swagger path definition');
@@ -138,7 +137,7 @@ public function assertResponseHeadersMatch(
 
         $constraint = new ResponseHeadersConstraint(
             $schemaManager->getResponseHeaders($template, $httpMethod, (string) $httpCode),
-            $this->getValidator()
+            self::getValidator()
         );
 
         Assert::assertThat($headers, $constraint, $message);
@@ -150,20 +149,20 @@ public function assertResponseHeadersMatch(
      * @param string[] $headers
      * @param string $path percent-encoded path used on the request.
      */
-    public function assertRequestHeadersMatch(
+    public static function assertRequestHeadersMatch(
         array $headers,
         SchemaManager $schemaManager,
         string $path,
         string $httpMethod,
         string $message = ''
-    ) {
+    ): void {
         if (!$schemaManager->findPathInTemplates($path, $template, $params)) {
             // @codeCoverageIgnoreStart
             throw new \RuntimeException('Request URI does not match with any swagger path definition');
             // @codeCoverageIgnoreEnd
         }
 
-        $constraint = new RequestHeadersConstraint($schemaManager->getRequestHeadersParameters($template, $httpMethod), $this->getValidator());
+        $constraint = new RequestHeadersConstraint($schemaManager->getRequestHeadersParameters($template, $httpMethod), self::getValidator());
 
         Assert::assertThat($headers, $constraint, $message);
     }
@@ -174,25 +173,25 @@ public function assertRequestHeadersMatch(
      * @param mixed[] $query
      * @param string $path percent-encoded path used on the request.
      */
-    public function assertRequestQueryMatch(
+    public static function assertRequestQueryMatch(
         $query,
         SchemaManager $schemaManager,
         string $path,
         string $httpMethod,
         string $message = ''
-    ) {
+    ): void {
         if (!$schemaManager->findPathInTemplates($path, $template, $params)) {
             // @codeCoverageIgnoreStart
             throw new \RuntimeException('Request URI does not match with any swagger path definition');
             // @codeCoverageIgnoreEnd
         }
 
-        $constraint = new RequestQueryConstraint($schemaManager->getRequestQueryParameters($template, $httpMethod), $this->getValidator());
+        $constraint = new RequestQueryConstraint($schemaManager->getRequestQueryParameters($template, $httpMethod), self::getValidator());
 
         Assert::assertThat($query, $constraint, $message);
     }
 
-    protected function getValidator(): Validator
+    protected static function getValidator(): Validator
     {
         return new Validator();
     }
diff --git a/src/PhpUnit/JsonSchemaConstraint.php b/src/PhpUnit/JsonSchemaConstraint.php
index 4c03b8a..bffdbb4 100644
--- a/src/PhpUnit/JsonSchemaConstraint.php
+++ b/src/PhpUnit/JsonSchemaConstraint.php
@@ -29,7 +29,9 @@ class JsonSchemaConstraint extends Constraint
 
     public function __construct($expectedSchema, string $context, Validator $validator)
     {
-        parent::__construct();
+        if (is_callable([Constraint::class, '__construct'])) {
+            parent::__construct();
+        }
 
         $this->expectedSchema = $expectedSchema;
         $this->context = $context;
diff --git a/src/PhpUnit/MediaTypeConstraint.php b/src/PhpUnit/MediaTypeConstraint.php
index 701b1a7..5281486 100644
--- a/src/PhpUnit/MediaTypeConstraint.php
+++ b/src/PhpUnit/MediaTypeConstraint.php
@@ -21,7 +21,9 @@ class MediaTypeConstraint extends Constraint
      */
     public function __construct(array $allowedMediaTypes)
     {
-        parent::__construct();
+        if (is_callable([Constraint::class, '__construct'])) {
+            parent::__construct();
+        }
 
         $this->allowedMediaTypes = $allowedMediaTypes;
     }
diff --git a/src/PhpUnit/Psr7AssertsTrait.php b/src/PhpUnit/Psr7AssertsTrait.php
index 18b82c7..6b81410 100644
--- a/src/PhpUnit/Psr7AssertsTrait.php
+++ b/src/PhpUnit/Psr7AssertsTrait.php
@@ -21,15 +21,15 @@ trait Psr7AssertsTrait
      *
      * @param string $path percent-encoded path used on the request.
      */
-    public function assertResponseMatch(
+    public static function assertResponseMatch(
         ResponseInterface $response,
         SchemaManager $schemaManager,
         string $path,
         string $httpMethod,
         string $message = ''
-    ) {
+    ): void {
         if (!empty((string) $response->getBody())) {
-            $this->assertResponseMediaTypeMatch(
+            self::assertResponseMediaTypeMatch(
                 $response->getHeaderLine('Content-Type'),
                 $schemaManager,
                 $path,
@@ -39,9 +39,9 @@ public function assertResponseMatch(
         }
 
         $httpCode = $response->getStatusCode();
-        $headers = $this->inlineHeaders($response->getHeaders());
+        $headers = self::inlineHeaders($response->getHeaders());
 
-        $this->assertResponseHeadersMatch(
+        self::assertResponseHeadersMatch(
             $headers,
             $schemaManager,
             $path,
@@ -50,7 +50,7 @@ public function assertResponseMatch(
             $message
         );
 
-        $this->assertResponseBodyMatch(
+        self::assertResponseBodyMatch(
             json_decode((string) $response->getBody()),
             $schemaManager,
             $path,
@@ -63,20 +63,20 @@ public function assertResponseMatch(
     /**
      * Asserts request match with the request schema.
      */
-    public function assertRequestMatch(
+    public static function assertRequestMatch(
         RequestInterface $request,
         SchemaManager $schemaManager,
         string $message = ''
-    ) {
+    ): void {
         $path = $request->getUri()->getPath();
         $httpMethod = $request->getMethod();
 
-        $headers = $this->inlineHeaders($request->getHeaders());
+        $headers = self::inlineHeaders($request->getHeaders());
 
         $queryString = $request->getUri()->getQuery();
         parse_str(html_entity_decode($queryString), $query);
 
-        $this->assertRequestHeadersMatch(
+        self::assertRequestHeadersMatch(
             $headers,
             $schemaManager,
             $path,
@@ -85,7 +85,7 @@ public function assertRequestMatch(
         );
 
         if (!empty((string) $request->getBody())) {
-            $this->assertRequestMediaTypeMatch(
+            self::assertRequestMediaTypeMatch(
                 $request->getHeaderLine('Content-Type'),
                 $schemaManager,
                 $path,
@@ -94,7 +94,7 @@ public function assertRequestMatch(
             );
         }
 
-        $this->assertRequestQueryMatch(
+        self::assertRequestQueryMatch(
             $query,
             $schemaManager,
             $path,
@@ -102,7 +102,7 @@ public function assertRequestMatch(
             $message
         );
 
-        $this->assertRequestBodyMatch(
+        self::assertRequestBodyMatch(
             json_decode((string) $request->getBody()),
             $schemaManager,
             $path,
@@ -114,14 +114,14 @@ public function assertRequestMatch(
     /**
      * Asserts response match with the response schema.
      */
-    public function assertResponseAndRequestMatch(
+    public static function assertResponseAndRequestMatch(
         ResponseInterface $response,
         RequestInterface $request,
         SchemaManager $schemaManager,
         string $message = ''
-    ) {
+    ): void {
         try {
-            $this->assertRequestMatch($request, $schemaManager, $message);
+            self::assertRequestMatch($request, $schemaManager, $message);
         } catch (ExpectationFailedException $e) {
             // If response represent a Client error then ignore.
             $statusCode = $response->getStatusCode();
@@ -130,7 +130,7 @@ public function assertResponseAndRequestMatch(
             }
         }
 
-        $this->assertResponseMatch($response, $schemaManager, $request->getUri()->getPath(), $request->getMethod(), $message);
+        self::assertResponseMatch($response, $schemaManager, $request->getUri()->getPath(), $request->getMethod(), $message);
     }
 
     /**
@@ -138,7 +138,7 @@ public function assertResponseAndRequestMatch(
      *
      * @return string[]
      */
-    protected function inlineHeaders(array $headers): array
+    protected static function inlineHeaders(array $headers): array
     {
         return array_map(
             function (array $headers) {
diff --git a/src/PhpUnit/SymfonyAssertsTrait.php b/src/PhpUnit/SymfonyAssertsTrait.php
index aedf019..f02714c 100644
--- a/src/PhpUnit/SymfonyAssertsTrait.php
+++ b/src/PhpUnit/SymfonyAssertsTrait.php
@@ -21,15 +21,15 @@ trait SymfonyAssertsTrait
      *
      * @param string $path percent-encoded path used on the request.
      */
-    public function assertResponseMatch(
+    public static function assertResponseMatch(
         Response $response,
         SchemaManager $schemaManager,
         string $path,
         string $httpMethod,
         string $message = ''
-    ) {
+    ): void {
         if (!empty((string) $response->getContent())) {
-            $this->assertResponseMediaTypeMatch(
+            self::assertResponseMediaTypeMatch(
                 $response->headers->get('Content-Type'),
                 $schemaManager,
                 $path,
@@ -39,9 +39,9 @@ public function assertResponseMatch(
         }
 
         $httpCode = $response->getStatusCode();
-        $headers = $this->inlineHeaders($response->headers->all());
+        $headers = self::inlineHeaders($response->headers->all());
 
-        $this->assertResponseHeadersMatch(
+        self::assertResponseHeadersMatch(
             $headers,
             $schemaManager,
             $path,
@@ -50,7 +50,7 @@ public function assertResponseMatch(
             $message
         );
 
-        $this->assertResponseBodyMatch(
+        self::assertResponseBodyMatch(
             json_decode($response->getContent()),
             $schemaManager,
             $path,
@@ -63,18 +63,18 @@ public function assertResponseMatch(
     /**
      * Asserts request match with the request schema.
      */
-    public function assertRequestMatch(
+    public static function assertRequestMatch(
         Request $request,
         SchemaManager $schemaManager,
         string $message = ''
-    ) {
+    ): void {
         $path = $request->getPathInfo();
         $httpMethod = $request->getMethod();
         $query = $request->query->all();
 
-        $headers = $this->inlineHeaders($request->headers->all());
+        $headers = self::inlineHeaders($request->headers->all());
 
-        $this->assertRequestHeadersMatch(
+        self::assertRequestHeadersMatch(
             $headers,
             $schemaManager,
             $path,
@@ -83,7 +83,7 @@ public function assertRequestMatch(
         );
 
         if (!empty((string) $request->getContent())) {
-            $this->assertRequestMediaTypeMatch(
+            self::assertRequestMediaTypeMatch(
                 $request->headers->get('Content-Type'),
                 $schemaManager,
                 $path,
@@ -92,7 +92,7 @@ public function assertRequestMatch(
             );
         }
 
-        $this->assertRequestQueryMatch(
+        self::assertRequestQueryMatch(
             $query,
             $schemaManager,
             $path,
@@ -100,7 +100,7 @@ public function assertRequestMatch(
             $message
         );
 
-        $this->assertRequestBodyMatch(
+        self::assertRequestBodyMatch(
             json_decode($request->getContent()),
             $schemaManager,
             $path,
@@ -112,14 +112,14 @@ public function assertRequestMatch(
     /**
      * Asserts response match with the response schema.
      */
-    public function assertResponseAndRequestMatch(
+    public static function assertResponseAndRequestMatch(
         Response $response,
         Request $request,
         SchemaManager $schemaManager,
         string $message = ''
-    ) {
+    ): void {
         try {
-            $this->assertRequestMatch($request, $schemaManager, $message);
+            self::assertRequestMatch($request, $schemaManager, $message);
         } catch (ExpectationFailedException $e) {
             // If response represent a Client error then ignore.
             $statusCode = $response->getStatusCode();
@@ -128,7 +128,7 @@ public function assertResponseAndRequestMatch(
             }
         }
 
-        $this->assertResponseMatch($response, $schemaManager, $request->getRequestUri(), $request->getMethod(), $message);
+        self::assertResponseMatch($response, $schemaManager, $request->getRequestUri(), $request->getMethod(), $message);
     }
 
     /**
@@ -136,7 +136,7 @@ public function assertResponseAndRequestMatch(
      *
      * @return string[]
      */
-    protected function inlineHeaders(array $headers): array
+    protected static function inlineHeaders(array $headers): array
     {
         return array_map(
             function (array $headers) {
diff --git a/tests/PhpUnit/AssertsTraitTest.php b/tests/PhpUnit/AssertsTraitTest.php
index 63dd30c..790114d 100644
--- a/tests/PhpUnit/AssertsTraitTest.php
+++ b/tests/PhpUnit/AssertsTraitTest.php
@@ -20,12 +20,12 @@ class AssertsTraitTest extends TestCase
      */
     protected $schemaManager;
 
-    protected function setUp()
+    protected function setUp(): void
     {
         $this->schemaManager = SchemaManager::fromUri('file://' . __DIR__ . '/../fixture/petstore-with-external-docs.json');
     }
 
-    public function testAssertResponseBodyMatch()
+    public function testAssertResponseBodyMatch(): void
     {
         $response = <<<'JSON'
 {
@@ -38,14 +38,14 @@ public function testAssertResponseBodyMatch()
         self::assertResponseBodyMatch($response, $this->schemaManager, '/api/pets/123456789', 'get', 200);
     }
 
-    public function testAssertResponseBodyMatchWithFile()
+    public function testAssertResponseBodyMatchWithFile(): void
     {
         $valid_gif_file = base64_decode('R0lGODlhAQABAAD/ACwAAAAAAQABAAACADs=', true);
 
         self::assertResponseBodyMatch($valid_gif_file, $this->schemaManager, '/api/pets/123456789/photo', 'get', 200);
     }
 
-    public function testAssertResponseBodyMatchFail()
+    public function testAssertResponseBodyMatchFail(): void
     {
         $response = <<<'JSON'
 [
@@ -64,12 +64,12 @@ public function testAssertResponseBodyMatchFail()
         }
     }
 
-    public function testValidResponseMediaType()
+    public function testValidResponseMediaType(): void
     {
         self::assertResponseMediaTypeMatch('text/html', $this->schemaManager, '/api/pets', 'get');
     }
 
-    public function testInvalidResponseMediaType()
+    public function testInvalidResponseMediaType(): void
     {
         try {
             self::assertResponseMediaTypeMatch('application/pdf', $this->schemaManager, '/api/pets', 'get');
@@ -79,7 +79,7 @@ public function testInvalidResponseMediaType()
         }
     }
 
-    public function testValidResponseHeaders()
+    public function testValidResponseHeaders(): void
     {
         $headers = [
             'ETag' => '123',
@@ -88,7 +88,7 @@ public function testValidResponseHeaders()
         self::assertResponseHeadersMatch($headers, $this->schemaManager, '/api/pets', 'get', 200);
     }
 
-    public function testInvalidResponseHeaders()
+    public function testInvalidResponseHeaders(): void
     {
         $headers = [];
 
@@ -100,7 +100,7 @@ public function testInvalidResponseHeaders()
         }
     }
 
-    public function testAssertRequestBodyMatch()
+    public function testAssertRequestBodyMatch(): void
     {
         $request = <<<'JSON'
 {
@@ -113,7 +113,7 @@ public function testAssertRequestBodyMatch()
         self::assertRequestBodyMatch($request, $this->schemaManager, '/api/pets', 'post');
     }
 
-    public function testAssertRequestBodyMatchFail()
+    public function testAssertRequestBodyMatchFail(): void
     {
         $request = <<<'JSON'
 {
@@ -130,12 +130,12 @@ public function testAssertRequestBodyMatchFail()
         }
     }
 
-    public function testValidRequestMediaType()
+    public function testValidRequestMediaType(): void
     {
         self::assertRequestMediaTypeMatch('application/json', $this->schemaManager, '/api/pets', 'post');
     }
 
-    public function testInvalidRequestMediaType()
+    public function testInvalidRequestMediaType(): void
     {
         try {
             self::assertRequestMediaTypeMatch('application/pdf', $this->schemaManager, '/api/pets', 'post');
@@ -145,7 +145,7 @@ public function testInvalidRequestMediaType()
         }
     }
 
-    public function testValidRequestHeaders()
+    public function testValidRequestHeaders(): void
     {
         $headers = [
             'X-Required-Header' => 'any',
@@ -154,7 +154,7 @@ public function testValidRequestHeaders()
         self::assertRequestHeadersMatch($headers, $this->schemaManager, '/api/pets/1234', 'patch');
     }
 
-    public function testInvalidRequestHeaders()
+    public function testInvalidRequestHeaders(): void
     {
         $headers = [];
 
@@ -166,14 +166,14 @@ public function testInvalidRequestHeaders()
         }
     }
 
-    public function testValidRequestQuery()
+    public function testValidRequestQuery(): void
     {
         $query = ['tags' => ['foo', 'bar'], 'limit' => 1];
 
         self::assertRequestQueryMatch($query, $this->schemaManager, '/api/pets', 'get');
     }
 
-    public function testInvalidRequestQuery()
+    public function testInvalidRequestQuery(): void
     {
         $query = ['tags' => ['foo', 'bar']];
 
diff --git a/tests/PhpUnit/JsonSchemaConstraintTest.php b/tests/PhpUnit/JsonSchemaConstraintTest.php
index 094d7ab..e83385d 100644
--- a/tests/PhpUnit/JsonSchemaConstraintTest.php
+++ b/tests/PhpUnit/JsonSchemaConstraintTest.php
@@ -20,7 +20,7 @@ class JsonSchemaConstraintTest extends TestCase
      */
     protected $constraint;
 
-    protected function setUp()
+    protected function setUp(): void
     {
         $schema = <<<JSON
 {
@@ -38,13 +38,13 @@ protected function setUp()
         $this->constraint = new JsonSchemaConstraint($schema, 'context', new Validator());
     }
 
-    public function testConstraintDefinition()
+    public function testConstraintDefinition(): void
     {
         self::assertCount(1, $this->constraint);
         self::assertEquals('is a valid context', $this->constraint->toString());
     }
 
-    public function testValidSchema()
+    public function testValidSchema(): void
     {
         $response = <<<'JSON'
 [
@@ -59,7 +59,7 @@ public function testValidSchema()
         self::assertTrue($this->constraint->evaluate($response, '', true));
     }
 
-    public function testInvalidSchema()
+    public function testInvalidSchema(): void
     {
         $response = <<<'JSON'
 [
diff --git a/tests/PhpUnit/MediaTypeConstraintTest.php b/tests/PhpUnit/MediaTypeConstraintTest.php
index 9a37190..80eb394 100644
--- a/tests/PhpUnit/MediaTypeConstraintTest.php
+++ b/tests/PhpUnit/MediaTypeConstraintTest.php
@@ -19,23 +19,23 @@ class MediaTypeConstraintTest extends TestCase
      */
     protected $constraint;
 
-    protected function setUp()
+    protected function setUp(): void
     {
         $this->constraint = new MediaTypeConstraint(['application/json', 'text/xml']);
     }
 
-    public function testConstraintDefinition()
+    public function testConstraintDefinition(): void
     {
         self::assertCount(1, $this->constraint);
         self::assertEquals('is an allowed media type (application/json, text/xml)', $this->constraint->toString());
     }
 
-    public function testValidMediaType()
+    public function testValidMediaType(): void
     {
         self::assertTrue($this->constraint->evaluate('text/xml', '', true));
     }
 
-    public function testInvalidMediaType()
+    public function testInvalidMediaType(): void
     {
         $mediaType = 'application/pdf';
         self::assertFalse($this->constraint->evaluate($mediaType, '', true));
diff --git a/tests/PhpUnit/Psr7AssertsTraitTest.php b/tests/PhpUnit/Psr7AssertsTraitTest.php
index cbbb505..0b0dd92 100644
--- a/tests/PhpUnit/Psr7AssertsTraitTest.php
+++ b/tests/PhpUnit/Psr7AssertsTraitTest.php
@@ -6,8 +6,8 @@
 
 use FR3D\SwaggerAssertions\SchemaManager;
 use PHPUnit\Framework\ExpectationFailedException;
+use PHPUnit\Framework\MockObject\MockObject;
 use PHPUnit\Framework\TestCase;
-use PHPUnit_Framework_MockObject_MockObject as MockObject;
 use Psr\Http\Message\RequestInterface;
 use Psr\Http\Message\ResponseInterface;
 use Psr\Http\Message\StreamInterface;
@@ -25,19 +25,19 @@ class Psr7AssertsTraitTest extends TestCase
      */
     protected $schemaManager;
 
-    protected function setUp()
+    protected function setUp(): void
     {
         $this->schemaManager = SchemaManager::fromUri('file://' . __DIR__ . '/../fixture/petstore-with-external-docs.json');
     }
 
-    public function testAssertResponseMatch()
+    public function testAssertResponseMatch(): void
     {
         $response = $this->createMockResponse(200, $this->getValidHeaders(), $this->getValidResponseBody());
 
         self::assertResponseMatch($response, $this->schemaManager, '/api/pets', 'get');
     }
 
-    public function testAssertResponseAndRequestMatch()
+    public function testAssertResponseAndRequestMatch(): void
     {
         $body = $this->getValidRequestBody();
         $response = $this->createMockResponse(200, $this->getValidHeaders(), $body);
@@ -46,7 +46,7 @@ public function testAssertResponseAndRequestMatch()
         self::assertResponseAndRequestMatch($response, $request, $this->schemaManager);
     }
 
-    public function testAssertResponseIsValidIfClientErrorAndRequestIsInvalid()
+    public function testAssertResponseIsValidIfClientErrorAndRequestIsInvalid(): void
     {
         $response = $this->createMockResponse(404, $this->getValidHeaders(), '{"code":400,"message":"Invalid"}');
         $request = $this->createMockRequest('POST', '/api/pets', ['Content-Type' => ['application/pdf']]);
@@ -54,7 +54,7 @@ public function testAssertResponseIsValidIfClientErrorAndRequestIsInvalid()
         self::assertResponseAndRequestMatch($response, $request, $this->schemaManager);
     }
 
-    public function testAssertRequestIsInvalidIfResponseIsNotAClientError()
+    public function testAssertRequestIsInvalidIfResponseIsNotAClientError(): void
     {
         $response = $this->createMockResponse(200, $this->getValidHeaders(), $this->getValidResponseBody());
         $request = $this->createMockRequest('POST', '/api/pets', ['Content-Type' => ['application/pdf']]);
@@ -62,11 +62,11 @@ public function testAssertRequestIsInvalidIfResponseIsNotAClientError()
         try {
             self::assertResponseAndRequestMatch($response, $request, $this->schemaManager);
         } catch (ExpectationFailedException $e) {
-            self::assertContains('request', $e->getMessage());
+            self::assertStringContainsString('request', $e->getMessage());
         }
     }
 
-    public function testAssertResponseBodyDoesNotMatch()
+    public function testAssertResponseBodyDoesNotMatch(): void
     {
         $response = <<<'JSON'
 [
@@ -93,7 +93,7 @@ public function testAssertResponseBodyDoesNotMatch()
         }
     }
 
-    public function testAssertResponseMediaTypeDoesNotMatch()
+    public function testAssertResponseMediaTypeDoesNotMatch(): void
     {
         $response = $this->createMockResponse(
             200,
@@ -112,7 +112,7 @@ public function testAssertResponseMediaTypeDoesNotMatch()
         }
     }
 
-    public function testAssertResponseHeaderDoesNotMatch()
+    public function testAssertResponseHeaderDoesNotMatch(): void
     {
         $headers = [
             'Content-Type' => ['application/json'],
@@ -137,7 +137,7 @@ public function testAssertResponseHeaderDoesNotMatch()
         }
     }
 
-    public function testAssertRequestBodyDoesNotMatch()
+    public function testAssertRequestBodyDoesNotMatch(): void
     {
         $request = <<<'JSON'
 {
@@ -163,7 +163,7 @@ public function testAssertRequestBodyDoesNotMatch()
         }
     }
 
-    public function testAssertRequestMediaTypeDoesNotMatch()
+    public function testAssertRequestMediaTypeDoesNotMatch(): void
     {
         $request = $this->createMockRequest(
             'POST',
@@ -183,7 +183,7 @@ public function testAssertRequestMediaTypeDoesNotMatch()
         }
     }
 
-    public function testAssertRequestHeaderDoesNotMatch()
+    public function testAssertRequestHeaderDoesNotMatch(): void
     {
         $headers = [
             'Content-Type' => ['application/json'],
@@ -208,7 +208,7 @@ public function testAssertRequestHeaderDoesNotMatch()
         }
     }
 
-    public function testAssertRequestQueryDoesNotMatch()
+    public function testAssertRequestQueryDoesNotMatch(): void
     {
         $query = [
             'tags' => ['foo', '1'],
@@ -232,17 +232,14 @@ public function testAssertRequestQueryDoesNotMatch()
         }
     }
 
-    public function testEmptyResponse()
+    public function testEmptyResponse(): void
     {
         $response = $this->createMockResponse(204, ['Content-Type' => ['']], '');
 
         self::assertResponseMatch($response, $this->schemaManager, '/api/pets/1', 'delete');
     }
 
-    /**
-     * @return string
-     */
-    protected function getValidRequestBody()
+    protected function getValidRequestBody(): string
     {
         return <<<'JSON'
 {
@@ -252,10 +249,7 @@ protected function getValidRequestBody()
 JSON;
     }
 
-    /**
-     * @return string
-     */
-    protected function getValidResponseBody()
+    protected function getValidResponseBody(): string
     {
         return <<<'JSON'
 [
@@ -270,7 +264,7 @@ protected function getValidResponseBody()
     /**
      * @return string[]
      */
-    protected function getValidHeaders()
+    protected function getValidHeaders(): array
     {
         return [
             'Content-Type' => [
@@ -283,18 +277,15 @@ protected function getValidHeaders()
     }
 
     /**
-     * @param string $method
-     * @param string $path
      * @param string[] $headers
-     * @param string $body
      * @param mixed[] $query
      *
      * @return MockObject|RequestInterface
      */
-    protected function createMockRequest($method, $path, array $headers, $body = '', $query = [])
+    protected function createMockRequest(string $method, string $path, array $headers, string $body = '', $query = [])
     {
         /** @var UriInterface|MockObject $request */
-        $uri = $this->getMockBuilder('Psr\Http\Message\UriInterface')->getMock();
+        $uri = $this->getMockBuilder(UriInterface::class)->getMock();
         $uri->method('getPath')->willReturn($path);
         $uri->method('getQuery')->willReturn(http_build_query($query, '', '&'));
 
@@ -312,13 +303,11 @@ protected function createMockRequest($method, $path, array $headers, $body = '',
     }
 
     /**
-     * @param int $statusCode
      * @param string[] $headers
-     * @param string $body
      *
      * @return MockObject|ResponseInterface
      */
-    protected function createMockResponse($statusCode, array $headers, $body)
+    protected function createMockResponse(int $statusCode, array $headers, string $body)
     {
         $headersMap = $this->transformHeadersToMap($headers);
 
@@ -333,11 +322,9 @@ protected function createMockResponse($statusCode, array $headers, $body)
     }
 
     /**
-     * @param string $body
-     *
      * @return StreamInterface|MockObject
      */
-    protected function createMockStream($body)
+    protected function createMockStream(string $body)
     {
         /** @var StreamInterface|MockObject $stream */
         $stream = $this->getMockBuilder(StreamInterface::class)->getMock();
@@ -351,7 +338,7 @@ protected function createMockStream($body)
      *
      * @return array
      */
-    private function transformHeadersToMap(array $headers)
+    private function transformHeadersToMap(array $headers): array
     {
         $headersMap = [];
         foreach ($headers as $headerName => $headerValues) {
diff --git a/tests/PhpUnit/RequestHeadersConstraintTest.php b/tests/PhpUnit/RequestHeadersConstraintTest.php
index 6d0b5f0..3f3aa4d 100644
--- a/tests/PhpUnit/RequestHeadersConstraintTest.php
+++ b/tests/PhpUnit/RequestHeadersConstraintTest.php
@@ -19,22 +19,22 @@ class RequestHeadersConstraintTest extends TestCase
      * @var Constraint
      */
     protected $constraint;
-    const TEST_SCHEMA = '[{"name":"X-Required-Header","in":"header","description":"Required header","required":true,"type":"string"},{"name":"X-Optional-Header","in":"header","description":"Optional header","type":"string"}]';
+    private const TEST_SCHEMA = '[{"name":"X-Required-Header","in":"header","description":"Required header","required":true,"type":"string"},{"name":"X-Optional-Header","in":"header","description":"Optional header","type":"string"}]';
 
-    protected function setUp()
+    protected function setUp(): void
     {
         $schema = json_decode(self::TEST_SCHEMA);
 
         $this->constraint = new RequestHeadersConstraint($schema, new Validator());
     }
 
-    public function testConstraintDefinition()
+    public function testConstraintDefinition(): void
     {
         self::assertCount(1, $this->constraint);
         self::assertEquals('is a valid request header', $this->constraint->toString());
     }
 
-    public function testValidHeaders()
+    public function testValidHeaders(): void
     {
         $headers = [
             'X-Required-Header' => 'any',
@@ -43,7 +43,7 @@ public function testValidHeaders()
         self::assertTrue($this->constraint->evaluate($headers, '', true));
     }
 
-    public function testCaseInsensitiveValidHeaders()
+    public function testCaseInsensitiveValidHeaders(): void
     {
         $headers = [
             'X-required-HEADER' => 'application/json',
@@ -52,7 +52,7 @@ public function testCaseInsensitiveValidHeaders()
         self::assertTrue($this->constraint->evaluate($headers, '', true));
     }
 
-    public function testInvalidHeaderType()
+    public function testInvalidHeaderType(): void
     {
         $headers = [
             'X-Optional-Header' => 'any',
@@ -76,7 +76,7 @@ public function testInvalidHeaderType()
         }
     }
 
-    public function testSchemaUnchanged()
+    public function testSchemaUnchanged(): void
     {
         $schema = json_decode(self::TEST_SCHEMA);
         new RequestHeadersConstraint($schema, new Validator());
diff --git a/tests/PhpUnit/RequestQueryConstraintTest.php b/tests/PhpUnit/RequestQueryConstraintTest.php
index d03385d..73ce8b1 100644
--- a/tests/PhpUnit/RequestQueryConstraintTest.php
+++ b/tests/PhpUnit/RequestQueryConstraintTest.php
@@ -20,7 +20,7 @@ class RequestQueryConstraintTest extends TestCase
      */
     protected $constraint;
 
-    protected function setUp()
+    protected function setUp(): void
     {
         $schema = '[{"name":"tags","in":"query","description":"tags to filter by","required":false,"type":"array","items":{"type":"string"},"collectionFormat":"csv"},{"name":"limit","in":"query","description":"maximum number of results to return","required":true,"type":"integer","format":"int32"}]';
         $schema = json_decode($schema);
@@ -28,13 +28,13 @@ protected function setUp()
         $this->constraint = new RequestQueryConstraint($schema, new Validator());
     }
 
-    public function testConstraintDefinition()
+    public function testConstraintDefinition(): void
     {
         self::assertCount(1, $this->constraint);
         self::assertEquals('is a valid request query', $this->constraint->toString());
     }
 
-    public function testValidQuery()
+    public function testValidQuery(): void
     {
         $parameters = [
             'tags' => ['foo', 'bar'],
@@ -44,7 +44,7 @@ public function testValidQuery()
         self::assertTrue($this->constraint->evaluate($parameters, '', true));
     }
 
-    public function testInvalidParameterType()
+    public function testInvalidParameterType(): void
     {
         self::markTestSkipped('Is not possible to check types');
 
@@ -71,7 +71,7 @@ public function testInvalidParameterType()
         }
     }
 
-    public function testMissingParameter()
+    public function testMissingParameter(): void
     {
         $parameters = [
             'tags' => ['foo', 'bar'],
@@ -95,7 +95,7 @@ public function testMissingParameter()
         }
     }
 
-    public function testConstructorDoesNotAlterParameters()
+    public function testConstructorDoesNotAlterParameters(): void
     {
         $source = '[{"name":"tags","in":"query","description":"tags to filter by","required":false,"type":"array","items":{"type":"string"},"collectionFormat":"csv"},{"name":"limit","in":"query","description":"maximum number of results to return","required":true,"type":"integer","format":"int32"}]';
         $schema = json_decode($source);
diff --git a/tests/PhpUnit/ResponseHeadersConstraintTest.php b/tests/PhpUnit/ResponseHeadersConstraintTest.php
index b579d53..32394f5 100644
--- a/tests/PhpUnit/ResponseHeadersConstraintTest.php
+++ b/tests/PhpUnit/ResponseHeadersConstraintTest.php
@@ -20,7 +20,7 @@ class ResponseHeadersConstraintTest extends TestCase
      */
     protected $constraint;
 
-    protected function setUp()
+    protected function setUp(): void
     {
         $schema = '{"ETag":{"minimum":1}}';
         $schema = json_decode($schema);
@@ -28,13 +28,13 @@ protected function setUp()
         $this->constraint = new ResponseHeadersConstraint($schema, new Validator());
     }
 
-    public function testConstraintDefinition()
+    public function testConstraintDefinition(): void
     {
         self::assertCount(1, $this->constraint);
         self::assertEquals('is a valid response header', $this->constraint->toString());
     }
 
-    public function testValidHeaders()
+    public function testValidHeaders(): void
     {
         $headers = [
             'Content-Type' => 'application/json',
@@ -44,7 +44,7 @@ public function testValidHeaders()
         self::assertTrue($this->constraint->evaluate($headers, '', true));
     }
 
-    public function testCaseInsensitiveValidHeaders()
+    public function testCaseInsensitiveValidHeaders(): void
     {
         $headers = [
             'Content-Type' => 'application/json',
@@ -54,7 +54,7 @@ public function testCaseInsensitiveValidHeaders()
         self::assertTrue($this->constraint->evaluate($headers, '', true));
     }
 
-    public function testInvalidHeaderType()
+    public function testInvalidHeaderType(): void
     {
         $headers = [
             'Content-Type' => 'application/json',
diff --git a/tests/PhpUnit/SymfonyAssertsTraitTest.php b/tests/PhpUnit/SymfonyAssertsTraitTest.php
index 99a0f95..4c3e9d7 100644
--- a/tests/PhpUnit/SymfonyAssertsTraitTest.php
+++ b/tests/PhpUnit/SymfonyAssertsTraitTest.php
@@ -23,19 +23,19 @@ class SymfonyAssertsTraitTest extends TestCase
      */
     protected $schemaManager;
 
-    protected function setUp()
+    protected function setUp(): void
     {
         $this->schemaManager = SchemaManager::fromUri('file://' . __DIR__ . '/../fixture/petstore-with-external-docs.json');
     }
 
-    public function testAssertResponseMatch()
+    public function testAssertResponseMatch(): void
     {
         $response = $this->createMockResponse(200, $this->getValidHeaders(), $this->getValidResponseBody());
 
         self::assertResponseMatch($response, $this->schemaManager, '/api/pets', 'get');
     }
 
-    public function testAssertResponseAndRequestMatch()
+    public function testAssertResponseAndRequestMatch(): void
     {
         $body = $this->getValidRequestBody();
         $response = $this->createMockResponse(200, $this->getValidHeaders(), $body);
@@ -44,7 +44,7 @@ public function testAssertResponseAndRequestMatch()
         self::assertResponseAndRequestMatch($response, $request, $this->schemaManager);
     }
 
-    public function testAssertResponseIsValidIfClientErrorAndRequestIsInvalid()
+    public function testAssertResponseIsValidIfClientErrorAndRequestIsInvalid(): void
     {
         $response = $this->createMockResponse(404, $this->getValidHeaders(), '{"code":400,"message":"Invalid"}');
         $request = $this->createMockRequest('POST', '/api/pets', ['Content-Type' => ['application/pdf']]);
@@ -52,7 +52,7 @@ public function testAssertResponseIsValidIfClientErrorAndRequestIsInvalid()
         self::assertResponseAndRequestMatch($response, $request, $this->schemaManager);
     }
 
-    public function testAssertRequestIsInvalidIfResponseIsNotAClientError()
+    public function testAssertRequestIsInvalidIfResponseIsNotAClientError(): void
     {
         $response = $this->createMockResponse(200, $this->getValidHeaders(), $this->getValidResponseBody());
         $request = $this->createMockRequest('POST', '/api/pets', ['Content-Type' => ['application/pdf']]);
@@ -60,11 +60,11 @@ public function testAssertRequestIsInvalidIfResponseIsNotAClientError()
         try {
             self::assertResponseAndRequestMatch($response, $request, $this->schemaManager);
         } catch (ExpectationFailedException $e) {
-            self::assertContains('request', $e->getMessage());
+            self::assertStringContainsString('request', $e->getMessage());
         }
     }
 
-    public function testAssertResponseBodyDoesNotMatch()
+    public function testAssertResponseBodyDoesNotMatch(): void
     {
         $response = <<<'JSON'
 [
@@ -91,7 +91,7 @@ public function testAssertResponseBodyDoesNotMatch()
         }
     }
 
-    public function testAssertResponseMediaTypeDoesNotMatch()
+    public function testAssertResponseMediaTypeDoesNotMatch(): void
     {
         $response = $this->createMockResponse(
             200,
@@ -110,7 +110,7 @@ public function testAssertResponseMediaTypeDoesNotMatch()
         }
     }
 
-    public function testAssertResponseHeaderDoesNotMatch()
+    public function testAssertResponseHeaderDoesNotMatch(): void
     {
         $headers = [
             'Content-Type' => ['application/json'],
@@ -135,7 +135,7 @@ public function testAssertResponseHeaderDoesNotMatch()
         }
     }
 
-    public function testAssertRequestBodyDoesNotMatch()
+    public function testAssertRequestBodyDoesNotMatch(): void
     {
         $request = <<<'JSON'
 {
@@ -161,7 +161,7 @@ public function testAssertRequestBodyDoesNotMatch()
         }
     }
 
-    public function testAssertRequestMediaTypeDoesNotMatch()
+    public function testAssertRequestMediaTypeDoesNotMatch(): void
     {
         $request = $this->createMockRequest(
             'POST',
@@ -181,7 +181,7 @@ public function testAssertRequestMediaTypeDoesNotMatch()
         }
     }
 
-    public function testAssertRequestHeaderDoesNotMatch()
+    public function testAssertRequestHeaderDoesNotMatch(): void
     {
         $headers = [
             'Content-Type' => ['application/json'],
@@ -206,7 +206,7 @@ public function testAssertRequestHeaderDoesNotMatch()
         }
     }
 
-    public function testAssertRequestQueryDoesNotMatch()
+    public function testAssertRequestQueryDoesNotMatch(): void
     {
         $query = [
             'tags' => ['foo', '1'],
@@ -230,17 +230,14 @@ public function testAssertRequestQueryDoesNotMatch()
         }
     }
 
-    public function testEmptyResponse()
+    public function testEmptyResponse(): void
     {
         $response = $this->createMockResponse(204, ['Content-Type' => ['']], '');
 
         self::assertResponseMatch($response, $this->schemaManager, '/api/pets/1', 'delete');
     }
 
-    /**
-     * @return string
-     */
-    protected function getValidRequestBody()
+    protected function getValidRequestBody(): string
     {
         return <<<'JSON'
 {
@@ -250,10 +247,7 @@ protected function getValidRequestBody()
 JSON;
     }
 
-    /**
-     * @return string
-     */
-    protected function getValidResponseBody()
+    protected function getValidResponseBody(): string
     {
         return <<<'JSON'
 [
@@ -268,7 +262,7 @@ protected function getValidResponseBody()
     /**
      * @return string[]
      */
-    protected function getValidHeaders()
+    protected function getValidHeaders(): array
     {
         return [
             'Content-Type' => 'application/json',
@@ -277,15 +271,10 @@ protected function getValidHeaders()
     }
 
     /**
-     * @param string $method
-     * @param string $path
      * @param string[] $headers
-     * @param string $body
      * @param mixed[] $query
-     *
-     * @return Request
      */
-    protected function createMockRequest($method, $path, array $headers, $body = '', $query = [])
+    protected function createMockRequest(string $method, string $path, array $headers, string $body = '', $query = []): Request
     {
         $request = Request::create($path, $method, $query, [], [], [], $body);
         $request->headers = new HeaderBag($headers);
@@ -294,13 +283,9 @@ protected function createMockRequest($method, $path, array $headers, $body = '',
     }
 
     /**
-     * @param int $statusCode
      * @param string[] $headers
-     * @param string $body
-     *
-     * @return Response
      */
-    protected function createMockResponse($statusCode, array $headers, $body)
+    protected function createMockResponse(int $statusCode, array $headers, string $body): Response
     {
         return new Response($body, $statusCode, $headers);
     }
diff --git a/tests/SchemaManagerTest.php b/tests/SchemaManagerTest.php
index ccbb998..fbb2dbc 100644
--- a/tests/SchemaManagerTest.php
+++ b/tests/SchemaManagerTest.php
@@ -16,7 +16,7 @@ class SchemaManagerTest extends TestCase
      */
     protected $schemaManager;
 
-    protected function setUp()
+    protected function setUp(): void
     {
         $this->schemaManager = SchemaManager::fromUri('file://' . __DIR__ . '/fixture/petstore-with-external-docs.json');
     }
@@ -24,14 +24,14 @@ protected function setUp()
     /**
      * @dataProvider validPathsProvider
      */
-    public function testFindPathInTemplatesValid($requestPath, $expectedTemplate, array $expectedParameters)
+    public function testFindPathInTemplatesValid($requestPath, $expectedTemplate, array $expectedParameters): void
     {
         self::assertTrue($this->schemaManager->findPathInTemplates($requestPath, $path, $parameters));
         self::assertEquals($expectedTemplate, $path);
         self::assertEquals($expectedParameters, $parameters);
     }
 
-    public function validPathsProvider()
+    public function validPathsProvider(): array
     {
         $dataCases = [
             'integer' => ['/api/pets/1234', '/pets/{id}', ['id' => 1234]],
@@ -58,14 +58,14 @@ public function validPathsProvider()
     /**
      * @dataProvider responseMediaTypesProvider
      */
-    public function testGetResponseMediaType($path, $method, array $expectedMediaTypes)
+    public function testGetResponseMediaType($path, $method, array $expectedMediaTypes): void
     {
         $mediaTypes = $this->schemaManager->getResponseMediaTypes($path, $method);
 
         self::assertEquals($expectedMediaTypes, $mediaTypes);
     }
 
-    public function responseMediaTypesProvider()
+    public function responseMediaTypesProvider(): array
     {
         return [
             // Description => [path, method, expectedMediaTypes]
@@ -77,14 +77,14 @@ public function responseMediaTypesProvider()
     /**
      * @dataProvider responseSchemaProvider
      */
-    public function testGetResponseSchema($path, $method, $httpCode, $expectedSchema)
+    public function testGetResponseSchema($path, $method, $httpCode, $expectedSchema): void
     {
         $schema = $this->schemaManager->getResponseSchema($path, $method, (string) $httpCode);
 
         self::assertEquals($expectedSchema, json_encode($schema));
     }
 
-    public function responseSchemaProvider()
+    public function responseSchemaProvider(): array
     {
         $schema200 = '{"type":"array","items":{"type":"object","required":["id","name"],"externalDocs":{"description":"find more info here","url":"https:\/\/swagger.io\/about"},"properties":{"id":{"type":"integer","format":"int64"},"name":{"type":"string"},"tag":{"type":"string"}}}}';
         $schemaDefault = '{"type":"object","required":["code","message"],"properties":{"code":{"type":"integer","format":"int32"},"message":{"type":"string"}}}';
@@ -102,14 +102,14 @@ public function responseSchemaProvider()
     /**
      * @dataProvider responseHeadersProvider
      */
-    public function testGetResponseHeaders($path, $method, $httpCode, $expectedHeaders)
+    public function testGetResponseHeaders($path, $method, $httpCode, $expectedHeaders): void
     {
         $headers = $this->schemaManager->getResponseHeaders($path, $method, (string) $httpCode);
 
         self::assertEquals($expectedHeaders, json_encode($headers));
     }
 
-    public function responseHeadersProvider()
+    public function responseHeadersProvider(): array
     {
         $dataSet = [
             // Description => [path, method, httpCode, expectedHeaders]
@@ -123,14 +123,14 @@ public function responseHeadersProvider()
     /**
      * @dataProvider requestMediaTypesProvider
      */
-    public function testGetRequestMediaType($path, $method, array $expectedMediaTypes)
+    public function testGetRequestMediaType($path, $method, array $expectedMediaTypes): void
     {
         $mediaTypes = $this->schemaManager->getRequestMediaTypes($path, $method);
 
         self::assertEquals($expectedMediaTypes, $mediaTypes);
     }
 
-    public function requestMediaTypesProvider()
+    public function requestMediaTypesProvider(): array
     {
         return [
             // Description => [path, method, expectedMediaTypes]
@@ -142,14 +142,14 @@ public function requestMediaTypesProvider()
     /**
      * @dataProvider requestParameters
      */
-    public function testGetRequestParameters($path, $method, $expectedParameters)
+    public function testGetRequestParameters($path, $method, $expectedParameters): void
     {
         $parameters = $this->schemaManager->getRequestParameters($path, $method);
 
         self::assertEquals($expectedParameters, json_encode($parameters));
     }
 
-    public function requestParameters()
+    public function requestParameters(): array
     {
         $pets_id_shared_parameters = '[{"name":"id","in":"path","description":"ID of pet to fetch","required":true,"type":"integer","format":"int64"}';
         $pets_id_patch_parameters = $pets_id_shared_parameters . ',{"name":"X-Required-Header","in":"header","description":"Required header","required":true,"type":"string"},{"name":"X-Optional-Header","in":"header","description":"Optional header","type":"string"},{"name":"pet","in":"body","description":"Pet to update","required":true,"schema":{"type":"object","allOf":[{"type":"object","required":["id","name"],"externalDocs":{"description":"find more info here","url":"https:\/\/swagger.io\/about"},"properties":{"id":{"type":"integer","format":"int64"},"name":{"type":"string"},"tag":{"type":"string"}}},{"required":["id"],"properties":{"id":{"type":"integer","format":"int64"}}}]}}]';
@@ -169,14 +169,14 @@ public function requestParameters()
     /**
      * @dataProvider requestHeadersParameters
      */
-    public function testGetRequestHeadersParameters($path, $method, $expectedParameters)
+    public function testGetRequestHeadersParameters($path, $method, $expectedParameters): void
     {
         $parameters = $this->schemaManager->getRequestHeadersParameters($path, $method);
 
         self::assertEquals($expectedParameters, json_encode($parameters));
     }
 
-    public function requestHeadersParameters()
+    public function requestHeadersParameters(): array
     {
         $parameters = '[{"name":"X-Required-Header","in":"header","description":"Required header","required":true,"type":"string"},{"name":"X-Optional-Header","in":"header","description":"Optional header","type":"string"}]';
 
@@ -192,14 +192,14 @@ public function requestHeadersParameters()
     /**
      * @dataProvider requestBodyParameters
      */
-    public function testGetRequestBodyParameters($path, $method, $expectedParameters)
+    public function testGetRequestBodyParameters($path, $method, $expectedParameters): void
     {
         $parameters = $this->schemaManager->getRequestSchema($path, $method);
 
         self::assertEquals($expectedParameters, json_encode($parameters));
     }
 
-    public function requestBodyParameters()
+    public function requestBodyParameters(): array
     {
         $parameters = '{"type":"object","allOf":[{"type":"object","required":["id","name"],"externalDocs":{"description":"find more info here","url":"https:\/\/swagger.io\/about"},"properties":{"id":{"type":"integer","format":"int64"},"name":{"type":"string"},"tag":{"type":"string"}}},{"required":["id"],"properties":{"id":{"type":"integer","format":"int64"}}}]}';
 
@@ -215,14 +215,14 @@ public function requestBodyParameters()
     /**
      * @dataProvider requestQueryParameters
      */
-    public function testGetRequestQueryParameters($path, $method, $expectedParameters)
+    public function testGetRequestQueryParameters($path, $method, $expectedParameters): void
     {
         $parameters = $this->schemaManager->getRequestQueryParameters($path, $method);
 
         self::assertEquals($expectedParameters, json_encode($parameters));
     }
 
-    public function requestQueryParameters()
+    public function requestQueryParameters(): array
     {
         $parameters = '[{"name":"tags","in":"query","description":"tags to filter by","required":false,"type":"array","items":{"type":"string"},"collectionFormat":"csv"},{"name":"limit","in":"query","description":"maximum number of results to return","required":true,"type":"integer","format":"int32"}]';