Migrate phpunit config.

Author: hbgl

phpunit.xml

@@ -1,16 +1,15 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/6.4/phpunit.xsd"
+         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd"
          bootstrap="vendor/autoload.php"
          colors="true"
          verbose="true">
-    <testsuite name="Unit">
-        <directory suffix="Test.php">tests</directory>
-    </testsuite>
-
-    <filter>
-        <whitelist processUncoveredFilesFromWhitelist="true">
-            <directory suffix=".php">src</directory>
-        </whitelist>
-    </filter>
-</phpunit>
+  <coverage processUncoveredFiles="true">
+    <include>
+      <directory suffix=".php">src</directory>
+    </include>
+  </coverage>
+  <testsuite name="Unit">
+    <directory suffix="Test.php">tests</directory>
+  </testsuite>
+</phpunit>