Allow phpunit 9

composer.json

@@ -15,7 +15,7 @@
         "php": ">=7.2.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "8.5.38",
+        "phpunit/phpunit": "8.5.38 || ^9",
         "psr/log": "^1.1.4 || ^2 || ^3",
         "phpstan/phpstan": "^1.11.11",
         "phpstan/phpstan-phpunit": "^1.4",

phpunit.xml.dist

@@ -1,24 +1,24 @@
 <?xml version="1.0" encoding="UTF-8"?>
-
-<phpunit backupGlobals="false"
-         backupStaticAttributes="false"
-         colors="true"
-         convertErrorsToExceptions="true"
-         convertNoticesToExceptions="true"
-         convertWarningsToExceptions="true"
-         processIsolation="false"
-         stopOnFailure="false"
-         bootstrap="vendor/autoload.php"
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    backupGlobals="false"
+    backupStaticAttributes="false"
+    colors="true"
+    convertErrorsToExceptions="true"
+    convertNoticesToExceptions="true"
+    convertWarningsToExceptions="true"
+    processIsolation="false"
+    stopOnFailure="false"
+    bootstrap="vendor/autoload.php"
+    xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd"
 >
     <testsuites>
         <testsuite name="Signal Handler Test Suite">
             <directory>./tests/</directory>
         </testsuite>
     </testsuites>
-
-    <filter>
-        <whitelist>
+    <coverage>
+        <include>
             <directory>./src/</directory>
-        </whitelist>
-    </filter>
+        </include>
+    </coverage>
 </phpunit>