Update PHPUnit to version 9

In order to prepare PHP8 compatibility we should use the recent version of PHPUnit

composer.json

@@ -24,7 +24,7 @@
         "kub-at/php-simple-html-dom-parser": "^1.7"
     },
     "require-dev": {
-        "phpunit/phpunit": "~5.0",
+        "phpunit/phpunit": "~9.0",
         "doctrine/cache": "~1.0"
     },
     "suggest": {

phpunit.xml.dist

@@ -1,32 +1,22 @@
 <?xml version="1.0" encoding="utf-8"?>
-<phpunit backupGlobals="false"
-         backupStaticAttributes="false"
-         colors="true"
-         convertErrorsToExceptions="true"
-         convertNoticesToExceptions="true"
-         convertWarningsToExceptions="true"
-         processIsolation="false"
-         stopOnFailure="false"
-         syntaxCheck="false"
+<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="./tests/Caxy/Tests/TestInit.php"
->
-
-    <groups>
-        <exclude>
-            <group>performance</group>
-        </exclude>
-    </groups>
-
-    <testsuites>
-        <testsuite name="php-htmldiff Test Suite">
-            <directory>./tests/Caxy/Tests/HtmlDiff</directory>
-        </testsuite>
-    </testsuites>
-
-    <filter>
-        <whitelist processUncoveredFilesFromWhitelist="true">
-            <directory suffix=".php">./lib</directory>
-        </whitelist>
-    </filter>
-
+         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd">
+  <coverage processUncoveredFiles="true">
+    <include>
+      <directory suffix=".php">./lib</directory>
+    </include>
+  </coverage>
+  <groups>
+    <exclude>
+      <group>performance</group>
+    </exclude>
+  </groups>
+  <testsuites>
+    <testsuite name="php-htmldiff Test Suite">
+      <directory>./tests/Caxy/Tests/HtmlDiff</directory>
+    </testsuite>
+  </testsuites>
 </phpunit>

tests/Caxy/Tests/AbstractTest.php

@@ -2,7 +2,9 @@
 
 namespace Caxy\Tests;
 
-abstract class AbstractTest extends \PHPUnit_Framework_TestCase
+use PHPUnit\Framework\TestCase;
+
+abstract class AbstractTest extends TestCase
 {
     protected function stripExtraWhitespaceAndNewLines($text)
     {
@@ -14,4 +16,4 @@ protected function stripExtraWhitespaceAndNewLines($text)
             )
         );
     }
-}
+}

tests/Caxy/Tests/HtmlDiff/Functional/HTMLPurifierConfigTest.php

@@ -13,7 +13,7 @@ class HTMLPurifierConfigTest extends AbstractTest
      */
     protected $config;
 
-    public function setUp()
+    public function setUp() : void
     {
         $config = \HTMLPurifier_Config::createDefault();
 
@@ -73,4 +73,4 @@ public function testHtmlDiffConfigStatic()
         $diff->setHTMLPurifierConfig($this->config);
         $diff->build();
     }
-}
+}