diff --git a/.github/workflows/code-quality.yaml b/.github/workflows/code-quality.yaml
new file mode 100644
index 0000000..e23def5
--- /dev/null
+++ b/.github/workflows/code-quality.yaml
@@ -0,0 +1,39 @@
+name: Code Quality
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+
+jobs:
+  code-quality:
+    name: Code Quality
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        php: [ '7.2', '7.3' ]
+
+    steps:
+      - name: 'Init repository'
+        uses: actions/checkout@v2
+
+      - name: 'Setup PHP'
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php }}
+          extensions: xsl, swoole
+          tools: composer
+
+      - name: "Install dependencies"
+        run: composer install
+
+      - name: 'Tests unit'
+        run: composer tests-unit
+
+      - name: 'Tests examples'
+        run: composer tests-examples
+
+      - name: 'Static analysis'
+        run: composer static-analysis
diff --git a/composer.json b/composer.json
index dec075e..6309488 100644
--- a/composer.json
+++ b/composer.json
@@ -51,10 +51,10 @@
         "bin-dir": "bin/"
     },
     "scripts": {
-        "tests-unit": "./bin/phpunit --testsuite='Tornado Test Suite'",
-        "tests-examples": "./bin/phpunit --testsuite='Tornado Examples'",
-        "static-analysis": "./bin/phpstan analyse src tests --level=7 --no-progress -vvv",
-        "code-style-check": "./bin/php-cs-fixer fix --dry-run --verbose",
-        "code-style-fix": "./bin/php-cs-fixer fix"
+        "tests-unit": "@php ./bin/phpunit --testsuite='Tornado Test Suite'",
+        "tests-examples": "@php ./bin/phpunit --testsuite='Tornado Examples'",
+        "static-analysis": "@php ./bin/phpstan analyse src tests --level=7 --no-progress -vvv",
+        "code-style-check": "@php ./bin/php-cs-fixer fix --dry-run --verbose",
+        "code-style-fix": "@php ./bin/php-cs-fixer fix"
     }
 }
diff --git a/src/Adapter/Amp/EventLoop.php b/src/Adapter/Amp/EventLoop.php
index c20bc7f..5668fa3 100644
--- a/src/Adapter/Amp/EventLoop.php
+++ b/src/Adapter/Amp/EventLoop.php
@@ -11,7 +11,7 @@ class EventLoop implements \M6Web\Tornado\EventLoop
     /**
      * {@inheritdoc}
      */
-    public function wait(Promise $promise): mixed
+    public function wait(Promise $promise)
     {
         try {
             $result = \Amp\Promise\wait(
diff --git a/src/Adapter/ReactPhp/EventLoop.php b/src/Adapter/ReactPhp/EventLoop.php
index bd3e785..be89fa6 100644
--- a/src/Adapter/ReactPhp/EventLoop.php
+++ b/src/Adapter/ReactPhp/EventLoop.php
@@ -23,7 +23,7 @@ public function __construct(\React\EventLoop\LoopInterface $reactEventLoop)
     /**
      * {@inheritdoc}
      */
-    public function wait(Promise $promise): mixed
+    public function wait(Promise $promise)
     {
         $value = null;
         $isRejected = false;
diff --git a/src/Adapter/Swoole/EventLoop.php b/src/Adapter/Swoole/EventLoop.php
index 8fe33a2..d21078d 100644
--- a/src/Adapter/Swoole/EventLoop.php
+++ b/src/Adapter/Swoole/EventLoop.php
@@ -57,10 +57,10 @@ public function __destruct()
         //Event::exit();
     }
 
-    private function shiftCoroutine(): mixed
+    private function shiftCoroutine(): void
     {
         if (count($this->cids) === 0) {
-            return null;
+            return;
         }
 
         $cid = array_shift($this->cids);
@@ -70,17 +70,14 @@ private function shiftCoroutine(): mixed
         } else {
             $this->shiftCoroutine();
         }
-
-        return $cid;
     }
 
-    private function pushCoroutine(): mixed
+    private function pushCoroutine(): void
     {
         $cid = Coroutine::getCid();
         $this->cids[] = $cid;
         Coroutine::yield();
 
-        return $cid;
     }
 
     private function createPromise(): DummyPromise
@@ -144,7 +141,7 @@ private function isPending(DummyPromise $promise): bool
     /**
      * {@inheritdoc}
      */
-    public function wait(Promise $promise): mixed
+    public function wait(Promise $promise)
     {
         $promise = DummyPromise::wrap($promise);
 
diff --git a/src/Adapter/Swoole/Internal/DummyPromise.php b/src/Adapter/Swoole/Internal/DummyPromise.php
index f0be824..5d3be27 100644
--- a/src/Adapter/Swoole/Internal/DummyPromise.php
+++ b/src/Adapter/Swoole/Internal/DummyPromise.php
@@ -8,9 +8,24 @@
 
 final class DummyPromise implements Promise, Deferred
 {
-    private bool $isPending;
-    private mixed $value;
-    private ?Throwable $exception;
+    /**
+     * @var bool
+     */
+    private $isPending;
+
+    /**
+     * @var mixed
+     */
+    private $value;
+
+    /**
+     * @var Throwable|null
+     */
+    private $exception;
+
+    /**
+     * @var callable[]
+     */
     private $callbacks;
 
     public function __construct(?callable $callback = null)
@@ -43,6 +58,7 @@ public function resolve($value): void
 
         $this->isPending = false;
         $this->value = $value;
+
         foreach ($this->callbacks as $callback) {
             ($callback)($this);
         }
diff --git a/src/Adapter/Swoole/PromiseEventLoop.php b/src/Adapter/Swoole/PromiseEventLoop.php
index 0351531..748ebc8 100644
--- a/src/Adapter/Swoole/PromiseEventLoop.php
+++ b/src/Adapter/Swoole/PromiseEventLoop.php
@@ -33,7 +33,7 @@ public function __construct()
     /**
      * {@inheritdoc}
      */
-    public function wait(Promise $promise): mixed
+    public function wait(Promise $promise)
     {
         $value = null;
         $isRejected = false;
diff --git a/src/Adapter/Swoole/YieldEventLoop.php b/src/Adapter/Swoole/YieldEventLoop.php
index b6632ad..99c6300 100644
--- a/src/Adapter/Swoole/YieldEventLoop.php
+++ b/src/Adapter/Swoole/YieldEventLoop.php
@@ -23,7 +23,7 @@ public function __construct()
     /**
      * {@inheritdoc}
      */
-    public function wait(Promise $promise): mixed
+    public function wait(Promise $promise)
     {
         $value = null;
         $this->async((static function () use ($promise, &$value): \Generator {
diff --git a/src/Adapter/Tornado/EventLoop.php b/src/Adapter/Tornado/EventLoop.php
index 753a4a3..546c5d3 100644
--- a/src/Adapter/Tornado/EventLoop.php
+++ b/src/Adapter/Tornado/EventLoop.php
@@ -26,7 +26,7 @@ public function __construct()
     /**
      * {@inheritdoc}
      */
-    public function wait(Promise $promise): mixed
+    public function wait(Promise $promise)
     {
         $promiseIsPending = true;
         $finalAction = function () {throw new \Error('Impossible to resolve the promise, no more task to execute..'); };
diff --git a/src/Adapter/Tornado/SynchronousEventLoop.php b/src/Adapter/Tornado/SynchronousEventLoop.php
index 91a7852..21cd4f8 100644
--- a/src/Adapter/Tornado/SynchronousEventLoop.php
+++ b/src/Adapter/Tornado/SynchronousEventLoop.php
@@ -13,7 +13,7 @@ class SynchronousEventLoop implements \M6Web\Tornado\EventLoop
     /**
      * {@inheritdoc}
      */
-    public function wait(Promise $promise): mixed
+    public function wait(Promise $promise)
     {
         // If there are some uncaught exceptions, throw the first one.
         if ($throwable = reset($this->asyncThrowables)) {
diff --git a/src/EventLoop.php b/src/EventLoop.php
index 0f31af1..d93d742 100644
--- a/src/EventLoop.php
+++ b/src/EventLoop.php
@@ -7,8 +7,10 @@ interface EventLoop
     /**
      * Waits the resolution of a promise, and returns its value.
      * You should use this function once for your global result.
+     *
+     * @return mixed
      */
-    public function wait(Promise $promise): mixed;
+    public function wait(Promise $promise);
 
     /**
      * Registers a generator in the event loop to execute it asynchronously.