diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 5c44c780..413f166a 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -4,8 +4,9 @@
 <phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
          xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd"
          bootstrap="vendor/autoload.php"
+         cacheResult="false"
          colors="true"
-         cacheResult="false">
+         convertDeprecationsToExceptions="true">
     <testsuites>
         <testsuite name="Promise Test Suite">
             <directory>./tests/</directory>
@@ -19,4 +20,7 @@
             <file>./src/functions_include.php</file>
         </exclude>
     </coverage>
+    <php>
+        <ini name="error_reporting" value="-1" />
+    </php>
 </phpunit>
diff --git a/tests/Internal/RejectedPromiseTest.php b/tests/Internal/RejectedPromiseTest.php
index 028ca4dc..e2e7a15f 100644
--- a/tests/Internal/RejectedPromiseTest.php
+++ b/tests/Internal/RejectedPromiseTest.php
@@ -29,15 +29,15 @@ public function getPromiseTestAdapter(callable $canceller = null)
             'resolve' => function () {
                 throw new LogicException('You cannot call resolve() for React\Promise\RejectedPromise');
             },
-            'reject' => function ($reason = null) use (&$promise) {
+            'reject' => function (\Throwable $reason) use (&$promise) {
                 if (!$promise) {
                     $promise = new RejectedPromise($reason);
                 }
             },
-            'settle' => function ($reason = "") use (&$promise) {
+            'settle' => function ($reason = '') use (&$promise) {
                 if (!$promise) {
                     if (!$reason instanceof Exception) {
-                        $reason = new Exception($reason);
+                        $reason = new Exception((string) $reason);
                     }
 
                     $promise = new RejectedPromise($reason);