diff --git a/.travis.yml b/.travis.yml
index a0931eb..23364b9 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,19 +1,24 @@
 language: php
 
-matrix:
-  fast_finish: true
-  include:
-    - php: 5.5
-    - php: 5.6
-    - php: 7
-    - php: hhvm
-  allow_failures:
-    - php: 7
-    - php: hhvm
+php:
+  - 7.0
+  - 7.1
+  - 7.2
+
+env:
+  - COMPOSER_FLAGS=--prefer-lowest
+  - COMPOSER_FLAGS=
+
+before_install:
+  - phpenv config-rm xdebug.ini
 
 install:
-  - travis_retry composer install --no-interaction --ignore-platform-reqs --prefer-source
-  - composer info -i
+  - composer update --no-interaction --no-suggest --prefer-dist $COMPOSER_FLAGS
 
 script:
-  - ./vendor/bin/phpunit
+  - vendor/bin/phpunit
+
+cache:
+  directories:
+    - $HOME/.composer/cache
+    - vendor
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..301f924
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2017 PHP Middleware
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/README.md b/README.md
index c6c0e4a..e3379b2 100644
--- a/README.md
+++ b/README.md
@@ -1,33 +1,29 @@
 # log-http-messages middleware [![Build Status](https://travis-ci.org/php-middleware/log-http-messages.svg)](https://travis-ci.org/php-middleware/log-http-messages)
-Middleware for log PSR-7 HTTP messages using PSR-3 logger
+PSR-15 middleware for log PSR-7 HTTP messages using PSR-3 logger
 
 This middleware provide framework-agnostic possibility to log request and response messages to PSR-3 logger.
 
 ## Installation
 
-```json
-{
-    "require": {
-        "php-middleware/log-http-messages": "^2.0.0"
-    }
-}
+```
+composer require php-middleware/log-http-messages
 ```
 
-To log http messages you need pass into `LogRequestMiddleware` implementation of `PhpMiddleware\LogHttpMessages\Formatter\HttpMessagesFormatter`,
-instance `Psr\Log\LoggerInterface` and add middleware to your middleware runner.
-Third parameter is log level and it's optional (`Psr\Log\LogLevel::INFO` as default).
+To log http messages you need pass into `LogRequestMiddleware` implementation of
+`PhpMiddleware\LogHttpMessages\Formatter\ServerRequestFormatter`,
+`PhpMiddleware\LogHttpMessages\Formatter\ResponseFormatter`,
+instance `Psr\Log\LoggerInterface` and add this middleware to your middleware runner.
+You can also set log level (`Psr\Log\LogLevel::INFO` as default) and log message (`Request/Response` as default).
 
-There are tree implementation of `PhpMiddleware\LogHttpMessages\Formatter\HttpMessagesFormatter`:
+Provided implementation of formatters:
 
-* `PhpMiddleware\LogHttpMessages\Formatter\RequestFormatter` to log request message,
-* `PhpMiddleware\LogHttpMessages\Formatter\ResponseFormatter` to log response message,
-* `PhpMiddleware\LogHttpMessages\Formatter\BothFormatter` to log request and response message.
+* `PhpMiddleware\LogHttpMessages\Formatter\EmptyMessageFormatter`,
+* `PhpMiddleware\LogHttpMessages\Formatter\ZendDiactorosToArrayMessageFormatter`,
+* `PhpMiddleware\LogHttpMessages\Formatter\ZendDiactorosToStringMessageFormatter`.
 
 ```php
-$requestFormatter = PhpMiddleware\LogHttpMessages\Formatter\RequestFormatter();
-$responseFormatter = PhpMiddleware\LogHttpMessages\Formatter\ResponseFormatter();
-$formatter = new PhpMiddleware\LogHttpMessages\Formatter\BothFormatter(requestFormatter, responseFormatter);
-$logMiddleware = new PhpMiddleware\LogHttpMessages\LogMiddleware(formatter, $logger);
+$formatter = PhpMiddleware\LogHttpMessages\Formatter\ZendDiactorosToArrayMessageFormatter();
+$logMiddleware = new PhpMiddleware\LogHttpMessages\LogMiddleware($formatter, $formatter, $logger);
 
 $app = new MiddlewareRunner();
 $app->add($logMiddleware);
@@ -44,4 +40,4 @@ Middleware should works with:
 * [Slim 3.x](https://github.com/slimphp/Slim)
 * [zend-log 2.6](https://github.com/zendframework/zend-log)
 
-And any other modern framework [supported middlewares and PSR-7](https://mwop.net/blog/2015-01-08-on-http-middleware-and-psr-7.html) and [PSR-3 implementation](http://www.php-fig.org/psr/psr-3/) logger.
+And any other modern framework [supported PSR-15 middlewares and PSR-7](https://mwop.net/blog/2015-01-08-on-http-middleware-and-psr-7.html) and [PSR-3 implementation](http://www.php-fig.org/psr/psr-3/) logger.
diff --git a/composer.json b/composer.json
index dc25ecd..813df82 100644
--- a/composer.json
+++ b/composer.json
@@ -1,24 +1,27 @@
 {
     "name": "php-middleware/log-http-messages",
-    "description": "Request and response middleware logger with PSR-7 and PSR-3",
+    "description": "PSR-15 middleware for log PSR-7 HTTP messages using PSR-3 logger",
     "type": "library",
     "keywords": [
         "debug",
         "middleware",
         "psr",
         "psr-7",
+        "psr-15",
         "log",
         "logger",
         "psr-3"
     ],
     "require": {
-        "php": ">=5.5",
-        "psr/log": "^1.0.0",
+        "php": ">=7.0",
+        "psr/log": "^1.0",
         "psr/http-message": "^1.0",
-        "zendframework/zend-diactoros": "^1.1.3"
+        "psr/http-server-handler": "^1.0",
+        "psr/http-server-middleware": "^1.0",
+        "zendframework/zend-diactoros": "^1.4 || ^2.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^4.8.6"
+        "phpunit/phpunit": "^6.1"
     },
     "autoload": {
         "psr-4": {
diff --git a/src/Formatter/BothFormatter.php b/src/Formatter/BothFormatter.php
deleted file mode 100644
index ab95a2f..0000000
--- a/src/Formatter/BothFormatter.php
+++ /dev/null
@@ -1,36 +0,0 @@
-<?php
-
-namespace PhpMiddleware\LogHttpMessages\Formatter;
-
-use Psr\Http\Message\ResponseInterface;
-use Psr\Http\Message\ServerRequestInterface;
-
-final class BothFormatter implements HttpMessagesFormatter
-{
-    private $requestFormatter;
-    private $responseFormatter;
-
-    /**
-     * @param RequestFormatter $requestFormatter
-     * @param ResponseFormatter $responseFormatter
-     */
-    public function __construct(RequestFormatter $requestFormatter, ResponseFormatter $responseFormatter)
-    {
-        $this->requestFormatter = $requestFormatter;
-        $this->responseFormatter = $responseFormatter;
-    }
-
-    /**
-     * @param ServerRequestInterface $request
-     * @param ResponseInterface $response
-     *
-     * @return string
-     */
-    public function format(ServerRequestInterface $request, ResponseInterface $response)
-    {
-        $requestString = $this->requestFormatter->format($request, $response);
-        $reponseString = $this->responseFormatter->format($request, $response);
-
-        return sprintf('Request: %s; Response %s', $requestString, $reponseString);
-    }
-}
\ No newline at end of file
diff --git a/src/Formatter/EmptyMessageFormatter.php b/src/Formatter/EmptyMessageFormatter.php
new file mode 100644
index 0000000..94b13cf
--- /dev/null
+++ b/src/Formatter/EmptyMessageFormatter.php
@@ -0,0 +1,24 @@
+<?php
+
+declare (strict_types=1);
+
+namespace PhpMiddleware\LogHttpMessages\Formatter;
+
+use Psr\Http\Message\ResponseInterface;
+use Psr\Http\Message\ServerRequestInterface;
+
+/**
+ * @codeCoverageIgnore
+ */
+final class EmptyMessageFormatter implements ServerRequestFormatter, ResponseFormatter
+{
+    public function formatServerRequest(ServerRequestInterface $request): FormattedMessage
+    {
+        return FormattedMessage::createEmpty();
+    }
+
+    public function formatResponse(ResponseInterface $response): FormattedMessage
+    {
+        return FormattedMessage::createEmpty();
+    }
+}
diff --git a/src/Formatter/FormattedMessage.php b/src/Formatter/FormattedMessage.php
new file mode 100644
index 0000000..270322a
--- /dev/null
+++ b/src/Formatter/FormattedMessage.php
@@ -0,0 +1,39 @@
+<?php
+
+declare (strict_types=1);
+
+namespace PhpMiddleware\LogHttpMessages\Formatter;
+
+final class FormattedMessage
+{
+    private $value;
+
+    public static function fromString(string $value) : self
+    {
+        $instance = new self();
+        $instance->value = $value;
+
+        return $instance;
+    }
+
+    public static function fromArray(array $value) : self
+    {
+        $instance = new self();
+        $instance->value = $value;
+
+        return $instance;
+    }
+
+    public static function createEmpty() : self
+    {
+        return new self();
+    }
+
+    /**
+     * @return array|string|null
+     */
+    public function getValue()
+    {
+        return $this->value;
+    }
+}
diff --git a/src/Formatter/HttpMessagesFormatter.php b/src/Formatter/HttpMessagesFormatter.php
deleted file mode 100644
index df21cb1..0000000
--- a/src/Formatter/HttpMessagesFormatter.php
+++ /dev/null
@@ -1,17 +0,0 @@
-<?php
-
-namespace PhpMiddleware\LogHttpMessages\Formatter;
-
-use Psr\Http\Message\ResponseInterface;
-use Psr\Http\Message\ServerRequestInterface;
-
-interface HttpMessagesFormatter
-{
-    /**
-     * @param ServerRequestInterface $request
-     * @param ResponseInterface $response
-     *
-     * @return string
-     */
-    public function format(ServerRequestInterface $request, ResponseInterface $response);
-}
diff --git a/src/Formatter/RequestFormatter.php b/src/Formatter/RequestFormatter.php
deleted file mode 100644
index 8970cd8..0000000
--- a/src/Formatter/RequestFormatter.php
+++ /dev/null
@@ -1,15 +0,0 @@
-<?php
-
-namespace PhpMiddleware\LogHttpMessages\Formatter;
-
-use Psr\Http\Message\ResponseInterface;
-use Psr\Http\Message\ServerRequestInterface;
-use Zend\Diactoros\Request\Serializer;
-
-final class RequestFormatter implements HttpMessagesFormatter
-{
-    public function format(ServerRequestInterface $request, ResponseInterface $response)
-    {
-        return Serializer::toString($request);
-    }
-}
\ No newline at end of file
diff --git a/src/Formatter/ResponseFormatter.php b/src/Formatter/ResponseFormatter.php
index 50884a5..ddfc5f9 100644
--- a/src/Formatter/ResponseFormatter.php
+++ b/src/Formatter/ResponseFormatter.php
@@ -1,15 +1,12 @@
 <?php
 
+declare (strict_types=1);
+
 namespace PhpMiddleware\LogHttpMessages\Formatter;
 
 use Psr\Http\Message\ResponseInterface;
-use Psr\Http\Message\ServerRequestInterface;
-use Zend\Diactoros\Response\Serializer;
 
-final class ResponseFormatter implements HttpMessagesFormatter
+interface ResponseFormatter
 {
-    public function format(ServerRequestInterface $request, ResponseInterface $response)
-    {
-        return Serializer::toString($response);
-    }
+    public function formatResponse(ResponseInterface $response) : FormattedMessage;
 }
\ No newline at end of file
diff --git a/src/Formatter/ServerRequestFormatter.php b/src/Formatter/ServerRequestFormatter.php
new file mode 100644
index 0000000..5a7255d
--- /dev/null
+++ b/src/Formatter/ServerRequestFormatter.php
@@ -0,0 +1,12 @@
+<?php
+
+declare (strict_types=1);
+
+namespace PhpMiddleware\LogHttpMessages\Formatter;
+
+use Psr\Http\Message\ServerRequestInterface;
+
+interface ServerRequestFormatter
+{
+    public function formatServerRequest(ServerRequestInterface $request) : FormattedMessage;
+}
diff --git a/src/Formatter/ZendDiactorosToArrayMessageFormatter.php b/src/Formatter/ZendDiactorosToArrayMessageFormatter.php
new file mode 100644
index 0000000..b6bc9be
--- /dev/null
+++ b/src/Formatter/ZendDiactorosToArrayMessageFormatter.php
@@ -0,0 +1,28 @@
+<?php
+
+declare (strict_types=1);
+
+namespace PhpMiddleware\LogHttpMessages\Formatter;
+
+use Psr\Http\Message\ResponseInterface;
+use Psr\Http\Message\ServerRequestInterface;
+use Zend\Diactoros\Response\ArraySerializer as ResponseSerializer;
+use Zend\Diactoros\Request\ArraySerializer as RequestSerializer;
+
+final class ZendDiactorosToArrayMessageFormatter implements ServerRequestFormatter, ResponseFormatter
+{
+    public function formatResponse(ResponseInterface $response): FormattedMessage
+    {
+        $array = ResponseSerializer::toArray($response);
+
+        return FormattedMessage::fromArray($array);
+    }
+
+    public function formatServerRequest(ServerRequestInterface $request): FormattedMessage
+    {
+        $array = RequestSerializer::toArray($request);
+
+        return FormattedMessage::fromArray($array);
+    }
+
+}
diff --git a/src/Formatter/ZendDiactorosToStringMessageFormatter.php b/src/Formatter/ZendDiactorosToStringMessageFormatter.php
new file mode 100644
index 0000000..3468a8f
--- /dev/null
+++ b/src/Formatter/ZendDiactorosToStringMessageFormatter.php
@@ -0,0 +1,27 @@
+<?php
+
+declare (strict_types=1);
+
+namespace PhpMiddleware\LogHttpMessages\Formatter;
+
+use Psr\Http\Message\ResponseInterface;
+use Psr\Http\Message\ServerRequestInterface;
+use Zend\Diactoros\Response\Serializer as ResponseSerializer;
+use Zend\Diactoros\Request\Serializer as RequestSerializer;
+
+final class ZendDiactorosToStringMessageFormatter implements ServerRequestFormatter, ResponseFormatter
+{
+    public function formatResponse(ResponseInterface $response): FormattedMessage
+    {
+        $string = ResponseSerializer::toString($response);
+
+        return FormattedMessage::fromString($string);
+    }
+
+    public function formatServerRequest(ServerRequestInterface $request): FormattedMessage
+    {
+        $string = RequestSerializer::toString($request);
+
+        return FormattedMessage::fromString($string);
+    }
+}
diff --git a/src/LogMiddleware.php b/src/LogMiddleware.php
index c1d86e4..2ba6ee4 100644
--- a/src/LogMiddleware.php
+++ b/src/LogMiddleware.php
@@ -1,60 +1,55 @@
 <?php
 
+declare (strict_types=1);
+
 namespace PhpMiddleware\LogHttpMessages;
 
-use PhpMiddleware\LogHttpMessages\Formatter\HttpMessagesFormatter;
+use PhpMiddleware\LogHttpMessages\Formatter\ResponseFormatter;
+use PhpMiddleware\LogHttpMessages\Formatter\ServerRequestFormatter;
 use Psr\Http\Message\ResponseInterface as Response;
 use Psr\Http\Message\ServerRequestInterface as ServerRequest;
+use Psr\Http\Server\MiddlewareInterface;
+use Psr\Http\Server\RequestHandlerInterface;
 use Psr\Log\LoggerInterface as Logger;
 use Psr\Log\LogLevel;
 
-class LogMiddleware
+final class LogMiddleware implements MiddlewareInterface
 {
-    /**
-     * @var Logger
-     */
-    protected $logger;
-
-    /**
-     * @var int
-     */
-    protected $level;
-
-    /**
-     * @var HttpMessagesFormatter
-     */
-    protected $formatter;
-
-    /**
-     * @param LoggerInterface $logger
-     * @param int $level
-     */
-    public function __construct(HttpMessagesFormatter $formatter, Logger $logger, $level = LogLevel::INFO)
-    {
-        $this->formatter = $formatter;
+    const LOG_MESSAGE = 'Request/Response';
+
+    private $logger;
+    private $level;
+    private $requestFormatter;
+    private $responseFormatter;
+    private $logMessage;
+
+    public function __construct(
+        ServerRequestFormatter $requestFormatter,
+        ResponseFormatter $responseFormatter,
+        Logger $logger,
+        string $level = LogLevel::INFO,
+        string $logMessage = self::LOG_MESSAGE
+    ) {
+        $this->requestFormatter = $requestFormatter;
+        $this->responseFormatter = $responseFormatter;
         $this->logger = $logger;
         $this->level = $level;
+        $this->logMessage = $logMessage;
     }
 
-    /**
-     * @param ServerRequest $request
-     * @param Response $response
-     * @param callable $next
-     *
-     * @return ResponseInterface
-     */
-    public function __invoke(ServerRequest $request, Response $response, callable $next)
+    /** @inheritdoc */
+    public function process(ServerRequest $request, RequestHandlerInterface $handler): Response
     {
-        $outResponse = $next($request, $response);
-
-        $messages = $this->formatter->format($request, $outResponse);
+        $response = $handler->handle($request);
 
-        if (!is_string($messages)) {
-            throw new \UnexpectedValueException(sprintf('%s must return string', HttpMessagesFormatter::class));
-        }
+        $formattedRequest = $this->requestFormatter->formatServerRequest($request);
+        $formattedResponse = $this->responseFormatter->formatResponse($response);
 
-        $this->logger->log($this->level, $messages);
+        $this->logger->log($this->level, $this->logMessage, [
+            'request' => $formattedRequest->getValue(),
+            'response' => $formattedResponse->getValue(),
+        ]);
 
-        return $outResponse;
+        return $response;
     }
 }
diff --git a/test/Formatter/BothFormatterTest.php b/test/Formatter/BothFormatterTest.php
deleted file mode 100644
index d112bb3..0000000
--- a/test/Formatter/BothFormatterTest.php
+++ /dev/null
@@ -1,33 +0,0 @@
-<?php
-
-namespace PhpMiddlewareTest\LogHttpMessages\Formatter;
-
-use PhpMiddleware\LogHttpMessages\Formatter\BothFormatter;
-use PhpMiddleware\LogHttpMessages\Formatter\RequestFormatter;
-use PhpMiddleware\LogHttpMessages\Formatter\ResponseFormatter;
-use PHPUnit_Framework_TestCase;
-use Zend\Diactoros\Response;
-use Zend\Diactoros\ServerRequest;
-
-class BothFormatterTest extends PHPUnit_Framework_TestCase
-{
-    protected $formatter;
-
-    protected function setUp()
-    {
-        $requestFormatter = new RequestFormatter();
-        $responseFormatter = new ResponseFormatter();
-
-        $this->formatter = new BothFormatter($requestFormatter, $responseFormatter);
-    }
-
-    public function testFormatter()
-    {
-        $request = new ServerRequest([], [], 'https://github.com/php-middleware/log-http-messages', 'GET', 'php://input', ['Accept' => 'text/html']);
-        $response = new Response('php://memory', 500, ['Content-Type' => 'text/html']);
-
-        $result = $this->formatter->format($request, $response);
-
-        $this->assertSame("Request: GET /php-middleware/log-http-messages HTTP/1.1\r\nAccept: text/html; Response HTTP/1.1 500 Internal Server Error\r\nContent-Type: text/html", $result);
-    }
-}
\ No newline at end of file
diff --git a/test/Formatter/FormattedMessageTest.php b/test/Formatter/FormattedMessageTest.php
new file mode 100644
index 0000000..d17bebf
--- /dev/null
+++ b/test/Formatter/FormattedMessageTest.php
@@ -0,0 +1,30 @@
+<?php
+
+namespace PhpMiddlewareTest\LogHttpMessages\Formatter;
+
+use PhpMiddleware\LogHttpMessages\Formatter\FormattedMessage;
+use PHPUnit\Framework\TestCase;
+
+class FormattedMessageTest extends TestCase
+{
+    public function testCanCreateFromString()
+    {
+        $formattedMessage = FormattedMessage::fromString('foo');
+
+        $this->assertSame('foo', $formattedMessage->getValue());
+    }
+
+    public function testCanCreateFromArray()
+    {
+        $formattedMessage = FormattedMessage::fromArray(['boo' => 'baz']);
+
+        $this->assertSame(['boo' => 'baz'], $formattedMessage->getValue());
+    }
+
+    public function testCanCreateEmpty()
+    {
+        $formattedMessage = FormattedMessage::createEmpty();
+
+        $this->assertNull($formattedMessage->getValue());
+    }
+}
diff --git a/test/Formatter/ZendDiactorosToArrayMessageFormatterTest.php b/test/Formatter/ZendDiactorosToArrayMessageFormatterTest.php
new file mode 100644
index 0000000..722ae5d
--- /dev/null
+++ b/test/Formatter/ZendDiactorosToArrayMessageFormatterTest.php
@@ -0,0 +1,31 @@
+<?php
+
+namespace PhpMiddlewareTest\LogHttpMessages\Formatter;
+
+use PhpMiddleware\LogHttpMessages\Formatter\ZendDiactorosToArrayMessageFormatter;
+use PHPUnit\Framework\TestCase;
+use Zend\Diactoros\Response;
+use Zend\Diactoros\ServerRequest;
+
+class ZendDiactorosToArrayMessageFormatterTest extends TestCase
+{
+    public function testFormatRequestToArray()
+    {
+        $request = new ServerRequest();
+        $formatter = new ZendDiactorosToArrayMessageFormatter();
+
+        $formattedMessage = $formatter->formatServerRequest($request);
+
+        $this->assertInternalType('array', $formattedMessage->getValue());
+    }
+
+    public function testFormatResponeToArray()
+    {
+        $response = new Response();
+        $formatter = new ZendDiactorosToArrayMessageFormatter();
+
+        $formattedMessage = $formatter->formatResponse($response);
+
+        $this->assertInternalType('array', $formattedMessage->getValue());
+    }
+}
diff --git a/test/Formatter/ZendDiactorosToStringMessageFormatterTest.php b/test/Formatter/ZendDiactorosToStringMessageFormatterTest.php
new file mode 100644
index 0000000..3c4c511
--- /dev/null
+++ b/test/Formatter/ZendDiactorosToStringMessageFormatterTest.php
@@ -0,0 +1,31 @@
+<?php
+
+namespace PhpMiddlewareTest\LogHttpMessages\Formatter;
+
+use PhpMiddleware\LogHttpMessages\Formatter\ZendDiactorosToStringMessageFormatter;
+use PHPUnit\Framework\TestCase;
+use Zend\Diactoros\Response;
+use Zend\Diactoros\ServerRequest;
+
+class ZendDiactorosToStringMessageFormatterTest extends TestCase
+{
+    public function testFormatRequestToArray()
+    {
+        $request = new ServerRequest();
+        $formatter = new ZendDiactorosToStringMessageFormatter();
+
+        $formattedMessage = $formatter->formatServerRequest($request);
+
+        $this->assertInternalType('string', $formattedMessage->getValue());
+    }
+
+    public function testFormatResponeToArray()
+    {
+        $response = new Response();
+        $formatter = new ZendDiactorosToStringMessageFormatter();
+
+        $formattedMessage = $formatter->formatResponse($response);
+
+        $this->assertInternalType('string', $formattedMessage->getValue());
+    }
+}
diff --git a/test/LogMiddlewareTest.php b/test/LogMiddlewareTest.php
index f831734..cf0596a 100644
--- a/test/LogMiddlewareTest.php
+++ b/test/LogMiddlewareTest.php
@@ -2,62 +2,45 @@
 
 namespace PhpMiddlewareTest\LogHttpMessages;
 
-use PhpMiddleware\LogHttpMessages\Formatter\HttpMessagesFormatter;
+use PhpMiddleware\LogHttpMessages\Formatter\EmptyMessageFormatter;
 use PhpMiddleware\LogHttpMessages\LogMiddleware;
-use PHPUnit_Framework_TestCase;
+use PHPUnit\Framework\MockObject\MockObject;
+use PHPUnit\Framework\TestCase;
 use Psr\Http\Message\ResponseInterface;
 use Psr\Http\Message\ServerRequestInterface;
+use Psr\Http\Server\RequestHandlerInterface;
 use Psr\Log\LoggerInterface;
 use Psr\Log\LogLevel;
 
-class LogMiddlewareTest extends PHPUnit_Framework_TestCase
+class LogMiddlewareTest extends TestCase
 {
-    protected $middleware;
-    protected $formatter;
-    protected $logger;
-    protected $request;
-    protected $response;
-    protected $next;
-    protected $level;
+    /** @var LogMiddleware */
+    private $middleware;
+    /** @var LoggerInterface|MockObject */
+    private $logger;
+    private $handler;
 
     protected function setUp()
     {
-        $this->request = $this->getMock(ServerRequestInterface::class);
-        $this->response = $this->getMock(ResponseInterface::class);
-        $this->nextResponse = clone $this->response;
-        $this->next = function () {
-            return $this->nextResponse;
-        };
-
-        $this->formatter = $this->getMock(HttpMessagesFormatter::class);
-        $this->logger = $this->getMock(LoggerInterface::class);
-        $this->level = LogLevel::ALERT;
-
-        $this->middleware = new LogMiddleware($this->formatter, $this->logger, $this->level);
-    }
+        $response = $this->createMock(ResponseInterface::class);
 
-    public function testLogMessage()
-    {
-        $this->formatter->expects($this->once())->method('format')->with($this->request, $this->nextResponse)->willReturn('boo');
-        $this->logger->expects($this->once())->method('log')->with($this->level, 'boo');
+        $this->handler = $this->createMock(RequestHandlerInterface::class);
+        $this->handler->method('handle')->willReturn($response);
 
-        $response = $this->executeMiddleware();
+        $formatter = new EmptyMessageFormatter();
+        $this->logger = $this->createMock(LoggerInterface::class);
 
-        $this->assertSame($this->nextResponse, $response);
+        $this->middleware = new LogMiddleware($formatter, $formatter, $this->logger, LogLevel::ALERT);
     }
 
-    /**
-     * @expectedException \UnexpectedValueException
-     */
-    public function testTryToLogNullMessage()
+    public function testLogFormattedMessages()
     {
-        $this->formatter->expects($this->once())->method('format')->willReturn(null);
+        /** @var ServerRequestInterface|MockObject $request */
+        $request = $this->createMock(ServerRequestInterface::class);
 
-        $this->executeMiddleware();
-    }
+        $this->logger->expects($this->once())->method('log')
+            ->with(LogLevel::ALERT, LogMiddleware::LOG_MESSAGE, ['request' => null, 'response' => null]);
 
-    public function executeMiddleware()
-    {
-        return call_user_func($this->middleware, $this->request, $this->response, $this->next);
+        $this->middleware->process($request, $this->handler);
     }
-}
\ No newline at end of file
+}