diff --git a/application/FileUtils.php b/application/FileUtils.php
index ba40982..30560bf 100644
--- a/application/FileUtils.php
+++ b/application/FileUtils.php
@@ -1,8 +1,8 @@
 <?php
 
-use Shaarli\Exceptions\IOException;
+namespace Shaarli;
 
-require_once 'exceptions/IOException.php';
+use Shaarli\Exceptions\IOException;
 
 /**
  * Class FileUtils
@@ -46,7 +46,7 @@ class FileUtils
 
         return file_put_contents(
             $file,
-            self::$phpPrefix.base64_encode(gzdeflate(serialize($content))).self::$phpSuffix
+            self::$phpPrefix . base64_encode(gzdeflate(serialize($content))) . self::$phpSuffix
         );
     }
 
@@ -64,7 +64,7 @@ class FileUtils
     {
         // Note that gzinflate is faster than gzuncompress.
         // See: http://www.php.net/manual/en/function.gzdeflate.php#96439
-        if (! is_readable($file)) {
+        if (!is_readable($file)) {
             return $default;
         }
 
diff --git a/application/History.php b/application/History.php
index 8074a01..a584665 100644
--- a/application/History.php
+++ b/application/History.php
@@ -3,7 +3,6 @@ namespace Shaarli;
 
 use DateTime;
 use Exception;
-use FileUtils;
 
 /**
  * Class History
@@ -71,7 +70,7 @@ class History
      * History constructor.
      *
      * @param string $historyFilePath History file path.
-     * @param int    $retentionTime   History content rentention time in seconds.
+     * @param int    $retentionTime   History content retention time in seconds.
      *
      * @throws Exception if something goes wrong.
      */
@@ -146,7 +145,7 @@ class History
      * Save a new event and write it in the history file.
      *
      * @param string $status Event key, should be defined as constant.
-     * @param mixed $id Event item identifier (e.g. link ID).
+     * @param mixed  $id     Event item identifier (e.g. link ID).
      */
     protected function addEvent($status, $id = null)
     {
diff --git a/application/LinkDB.php b/application/LinkDB.php
index 87a53e2..a5b4272 100644
--- a/application/LinkDB.php
+++ b/application/LinkDB.php
@@ -1,6 +1,7 @@
 <?php
 
 use Shaarli\Exceptions\IOException;
+use Shaarli\FileUtils;
 
 /**
  * Data storage for links.
diff --git a/composer.json b/composer.json
index 28b0adb..422a3a4 100644
--- a/composer.json
+++ b/composer.json
@@ -16,6 +16,7 @@
     },
     "require": {
         "php": ">=5.6",
+        "ext-zlib": "*",
         "shaarli/netscape-bookmark-parser": "^2.1",
         "erusev/parsedown": "^1.6",
         "slim/slim": "^3.0",
diff --git a/tests/FileUtilsTest.php b/tests/FileUtilsTest.php
index 9596dba..5771917 100644
--- a/tests/FileUtilsTest.php
+++ b/tests/FileUtilsTest.php
@@ -1,15 +1,15 @@
 <?php
 
-use Shaarli\Exceptions\IOException;
+namespace Shaarli;
 
-require_once 'application/FileUtils.php';
+use Exception;
 
 /**
  * Class FileUtilsTest
  *
  * Test file utility class.
  */
-class FileUtilsTest extends PHPUnit_Framework_TestCase
+class FileUtilsTest extends \PHPUnit\Framework\TestCase
 {
     /**
      * @var string Test file path.
diff --git a/tests/HistoryTest.php b/tests/HistoryTest.php
index 7723c46..8303e53 100644
--- a/tests/HistoryTest.php
+++ b/tests/HistoryTest.php
@@ -4,7 +4,6 @@ namespace Shaarli;
 
 use DateTime;
 use Exception;
-use FileUtils;
 
 class HistoryTest extends \PHPUnit\Framework\TestCase
 {
diff --git a/tests/utils/ReferenceHistory.php b/tests/utils/ReferenceHistory.php
index f19cdf2..e411c41 100644
--- a/tests/utils/ReferenceHistory.php
+++ b/tests/utils/ReferenceHistory.php
@@ -1,5 +1,6 @@
 <?php
 
+use Shaarli\FileUtils;
 use Shaarli\History;
 
 /**