diff --git a/phpunit.xml b/phpunit.xml
index d3da7fa4..9a4b1524 100644
--- a/phpunit.xml
+++ b/phpunit.xml
@@ -1,18 +1,23 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd" bootstrap="resources/phpunit/bootstrap.php" colors="true" verbose="true" failOnWarning="true" cacheResult="false">
-  <testsuites>
-    <testsuite name="RdKafka FFI Bindings">
-      <directory suffix=".php">tests/</directory>
-    </testsuite>
-  </testsuites>
-  <coverage processUncoveredFiles="true">
-    <include>
-      <directory suffix=".php">src/</directory>
-    </include>
-    <exclude>
-      <file>src/constants.php</file>
-      <file>src/RdKafka/FFI/Methods.php</file>
-      <directory suffix=".php">src/RdKafka/FFI/Versions</directory>
-    </exclude>
-  </coverage>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd"
+         bootstrap="resources/phpunit/bootstrap.php"
+         colors="true" verbose="true"
+         failOnWarning="true"
+         cacheResult="false">
+    <testsuites>
+        <testsuite name="RdKafka FFI Bindings">
+            <directory suffix="Test.php">tests/</directory>
+        </testsuite>
+    </testsuites>
+    <coverage processUncoveredFiles="true">
+        <include>
+            <directory suffix=".php">src/</directory>
+        </include>
+        <exclude>
+            <file>src/constants.php</file>
+            <file>src/RdKafka/FFI/Methods.php</file>
+            <directory>src/RdKafka/FFI/Versions</directory>
+        </exclude>
+    </coverage>
 </phpunit>
diff --git a/resources/phpunit/bootstrap.php b/resources/phpunit/bootstrap.php
index a196517c..146cf6a7 100644
--- a/resources/phpunit/bootstrap.php
+++ b/resources/phpunit/bootstrap.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use RdKafka\FFI\Library;
 
 require __DIR__ . '/../../vendor/autoload.php';
diff --git a/tests/RdKafka/TopicConfTest.php b/tests/RdKafka/TopicConfTest.php
index fbfc6815..6d43c626 100644
--- a/tests/RdKafka/TopicConfTest.php
+++ b/tests/RdKafka/TopicConfTest.php
@@ -171,7 +171,7 @@ public function testSetPartitionerCbWithCallback(): void
         $topicConf = new TopicConf();
         $topicConf->setOpaque($expectedTopicOpaque);
         $topicConf->setPartitionerCb(
-            function (string $key, int $partitionCount, ?object $topic_opaque = null, ?object $message_opaque = null) use (&$callbackTopicOpaque, &$callbackMessageOpaque) {
+            function (?string $key, int $partitionCount, ?object $topic_opaque = null, ?object $message_opaque = null) use (&$callbackTopicOpaque, &$callbackMessageOpaque) {
                 $callbackTopicOpaque = $topic_opaque;
                 $callbackMessageOpaque = $message_opaque;
                 // force partition 2