Update PHPUnit configuration

Author: sebastianbergmann

.gitignore

@@ -3,4 +3,4 @@
 /.php-cs-fixer.php
 /.php-cs-fixer.cache
 /composer.lock
-/.phpunit.result.cache
+/.phpunit.cache

phpunit.xml

@@ -2,6 +2,7 @@
 <phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:noNamespaceSchemaLocation="vendor/phpunit/phpunit/phpunit.xsd"
          bootstrap="vendor/autoload.php"
+         cacheDirectory=".phpunit.cache"
          executionOrder="depends,defects"
          requireCoverageMetadata="true"
          beStrictAboutCoverageMetadata="true"
@@ -10,12 +11,14 @@
          failOnWarning="true"
          colors="true">
     <testsuites>
-        <testsuite name="default">
-            <directory suffix="Test.php">tests/unit</directory>
+        <testsuite name="unit">
+            <directory>tests/unit</directory>
         </testsuite>
     </testsuites>
 
-    <source>
+    <source restrictDeprecations="true"
+            restrictNotices="true"
+            restrictWarnings="true">
         <include>
             <directory>src</directory>
         </include>