diff --git a/.editorconfig b/.editorconfig
new file mode 100644
index 0000000..c70af76
--- /dev/null
+++ b/.editorconfig
@@ -0,0 +1,25 @@
+# EditorConfig is awesome: https://EditorConfig.org
+
+# top-most EditorConfig file
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+indent_style = space
+indent_size = 4
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[*.{md,htm,html,blade.php}]
+insert_final_newline = false
+trim_trailing_whitespace = false
+
+[*.{min.css,min.js}]
+insert_final_newline = false
+
+[*.{yml,yaml}]
+indent_size = 2
+
+[docker-compose.yml]
+indent_size = 4
diff --git a/.gitattributes b/.gitattributes
index dfe0770..ba7b5d2 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -1,2 +1,11 @@
 # Auto detect text files and perform LF normalization
 * text=auto
+
+/.github                 export-ignore
+/tests                   export-ignore
+.editorconfig            export-ignore
+.gitattributes           export-ignore
+.gitignore               export-ignore
+.php-cs-fixer.dist.php   export-ignore
+.travis.yml              export-ignore
+phpunit.xml              export-ignore
diff --git a/.gitignore b/.gitignore
index 61220af..9b50ea1 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,7 @@
 /vendor
-composer.phar
-composer.lock
+.phpunit.result.cache
 .php_cs.cache
+.php-cs-fixer.cache
 .DS_Store
+composer.phar
+composer.lock
diff --git a/README.md b/README.md
index 1cc2ff3..9091146 100644
--- a/README.md
+++ b/README.md
@@ -2,7 +2,6 @@
 [![Build Status](https://api.travis-ci.org/JackieDo/Xml-Array.svg?branch=master)](https://travis-ci.org/JackieDo/Xml-Array)
 [![Total Downloads](https://poser.pugx.org/jackiedo/xml-array/downloads)](https://packagist.org/packages/jackiedo/xml-array)
 [![Latest Stable Version](https://poser.pugx.org/jackiedo/xml-array/v/stable)](https://packagist.org/packages/jackiedo/xml-array)
-[![Latest Unstable Version](https://poser.pugx.org/jackiedo/xml-array/v/unstable)](https://packagist.org/packages/jackiedo/xml-array)
 [![License](https://poser.pugx.org/jackiedo/xml-array/license)](https://packagist.org/packages/jackiedo/xml-array)
 
 The conversion between xml and array becomes easier than ever. This package provides some very simple classes to convert XML to array and back.
@@ -15,30 +14,38 @@ The conversion between xml and array becomes easier than ever. This package prov
 # Overview
 Look at one of the following sessions to learn more about this package.
 
-* [Installation](#installation)
-* [Basic usage](#basic-usage)
+- [Xml-Array](#xml-array)
+- [Features of this package](#features-of-this-package)
+- [Overview](#overview)
+  - [Installation](#installation)
+  - [Basic usage](#basic-usage)
     - [Convert XML to array](#convert-xml-to-array)
     - [Convert XML to Json](#convert-xml-to-json)
     - [Convert array to XML](#convert-array-to-xml)
     - [Convert array to DOM](#convert-array-to-dom)
-* [Advanced usage](#advanced-usage)
+  - [Advanced usage](#advanced-usage)
     - [Set configuration](#set-configuration)
+      - [Method 1](#method-1)
+      - [Method 2](#method-2)
+      - [Method 3](#method-3)
     - [Get configuration](#get-configuration)
     - [Default configuration](#default-configuration)
-* [License](#license)
+      - [For Xml2Array](#for-xml2array)
+      - [For Array2Xml](#for-array2xml)
+- [License](#license)
 
 ## Installation
 You can install this package through [Composer](https://getcomposer.org).
 
 ```shell
-composer require jackiedo/xml-array
+$ composer require jackiedo/xml-array
 ```
 
 ## Basic usage
 
 ### Convert XML to array
 
-###### Syntax:
+**Syntax**:
 
 ```
 array Xml2Array::convert(DOMDocument|SimpleXMLElement|string $inputXML)->toArray();
@@ -46,7 +53,7 @@ array Xml2Array::convert(DOMDocument|SimpleXMLElement|string $inputXML)->toArray
 
 > **Note:** The input XML can be one of types DOMDocument object, SimpleXMLElement object or well-formed XML string.
 
-###### Example 1 (Convert from XML string):
+**Example 1** - _(Convert from XML string)_:
 
 ```php
 use Jackiedo\XmlArray\Xml2Array;
@@ -135,7 +142,7 @@ $array = [
 ]
 ```
 
-###### Example 2 (Convert form XML object, such as SimpleXMLElement):
+**Example 2** - _(Convert form XML object, such as SimpleXMLElement)_:
 
 ```php
 use Jackiedo\XmlArray\Xml2Array;
@@ -331,13 +338,13 @@ $array = [
 
 ### Convert XML to Json
 
-###### Syntax:
+**Syntax**:
 
 ```
 string Xml2Array::convert(DOMDocument|SimpleXMLElement|string $inputXML)->toJson([int $options = 0]);
 ```
 
-###### Example 3:
+**Example 3**:
 
 ```php
 $jsonString = Xml2Array::convert($xmlString)->toJson(JSON_UNESCAPED_UNICODE | JSON_PRETTY_PRINT);
@@ -345,13 +352,13 @@ $jsonString = Xml2Array::convert($xmlString)->toJson(JSON_UNESCAPED_UNICODE | JS
 
 ### Convert array to XML
 
-###### Syntax:
+**Syntax**:
 
 ```
 string Array2Xml::convert(array $array)->toXml([bool $prettyOutput = false]);
 ```
 
-###### Example 4:
+**Example 4**:
 
 ```php
 use Jackiedo\XmlArray\Array2Xml;
@@ -363,13 +370,13 @@ $xmlString = Array2Xml::convert($array)->toXml(true);
 
 ### Convert array to DOM
 
-###### Syntax:
+**Syntax**:
 
 ```
 DOMDocument Array2Xml::convert(array $array)->toDom();
 ```
 
-###### Example 5:
+**Example 5**:
 
 ```php
 $domObject = Array2Xml::convert($array)->toDom();
@@ -380,7 +387,7 @@ $domObject = Array2Xml::convert($array)->toDom();
 ### Set configuration
 You can set configuration for conversion process with one of following methods:
 
-###### Method 1:
+#### Method 1
 
 ```php
 ...
@@ -398,14 +405,14 @@ $xml = Array2Xml::convert($inputArray, $config)->toXml();
 
 > **Note**: Configuration is an array of parameters. For more details, see section [Default configuration](#default-configuration).
 
-###### Method 2:
+#### Method 2
 
 ```php
 $converter = new Xml2Array($config);
 $array     = $converter->convertFrom($inputXml)->toArray();
 ```
 
-###### Method 3:
+#### Method 3
 
 ```php
 $converter = new Xml2Array;
@@ -421,7 +428,7 @@ $config = $converter->getConfig();
 
 ### Default configuration
 
-###### For Xml2Array
+#### For Xml2Array
 
 ```php
 $defaultConfig = [
@@ -434,7 +441,7 @@ $defaultConfig = [
 ];
 ```
 
-###### For Array2Xml
+#### For Array2Xml
 
 ```php
 $defaultConfig = [
@@ -447,5 +454,5 @@ $defaultConfig = [
 ];
 ```
 
-## License
+# License
 [MIT](LICENSE) © Jackie Do
diff --git a/composer.json b/composer.json
index 39aea89..fb2ad52 100644
--- a/composer.json
+++ b/composer.json
@@ -32,7 +32,7 @@
     },
     "autoload": {
         "psr-4": {
-            "Jackiedo\\XmlArray\\": "src"
+            "Jackiedo\\XmlArray\\": "src/"
         }
     },
     "minimum-stability": "stable"
diff --git a/src/Array2Xml.php b/src/Array2Xml.php
index 5d31a32..e8857e9 100644
--- a/src/Array2Xml.php
+++ b/src/Array2Xml.php
@@ -1,42 +1,37 @@
-<?php namespace Jackiedo\XmlArray;
+<?php
+
+namespace Jackiedo\XmlArray;
 
 use DOMDocument;
 use DOMElement;
 use DOMException;
 
 /**
- * Array2Xml: A class to convert array in PHP to well-formed XML.
- * Throws an exception if the tag name or attribute name has invalid chars.
+ * A class to convert array in PHP to well-formed XML.
  *
- * Usage:
- *       $xml = Array2Xml::convert($array)->toXml();
- *       $xml = Array2Xml::convert($array, ['rootElement' => 'root_node'])->toXml();
- *       $dom = Array2Xml::convert($array)->toDom();
+ * @see https://github.com/JackieDo/Xml-Array/blob/master/README.md Documentation.
  *
- * @package xml-array
  * @author Jackie Do <anhvudo@gmail.com>
- * @copyright 2018
- * @version $Id$
- * @access public
+ * @license MIT
  */
 class Array2Xml
 {
     /**
-     * The configuration of the conversion
+     * The configuration of the conversion.
      *
      * @var array
      */
     protected $config = [];
 
     /**
-     * The working XML document
+     * The working XML document.
      *
      * @var DOMDocument
      */
-    protected $xml = null;
+    protected $xml;
 
     /**
-     * Constructor
+     * Constructor.
      *
      * @param array $config The configuration to use for this instance
      */
@@ -48,9 +43,9 @@ public function __construct(array $config = [])
     }
 
     /**
-     * Set configuration for converter
+     * Set configuration for converter.
      *
-     * @param  array  $config The configuration to use for conversion
+     * @param array $config The configuration to use for conversion
      *
      * @return $this
      */
@@ -71,7 +66,7 @@ public function setConfig(array $config = [])
     }
 
     /**
-     * Return configuration of converter
+     * Return configuration of converter.
      *
      * @return array
      */
@@ -82,12 +77,12 @@ public function getConfig()
 
     /**
      * Convert an array to an XML document
-     * A static facade for ease of use and backwards compatibility
+     * A static facade for ease of use and backwards compatibility.
      *
-     * @param  array $array  The input array
-     * @param  array $config The configuration to use for the conversion
+     * @param array $array  The input array
+     * @param array $config The configuration to use for the conversion
      *
-     * @return DOMDocument   The XML representation of the input array
+     * @return $this
      */
     public static function convert(array $array = [], array $config = [])
     {
@@ -97,9 +92,11 @@ public static function convert(array $array = [], array $config = [])
     }
 
     /**
-     * Convert an array to an XML document
+     * Convert an array to an XML document.
      *
-     * @param  array $array The input array
+     * @param array $array The input array
+     *
+     * @throws DOMException
      *
      * @return $this
      */
@@ -107,7 +104,7 @@ public function convertFrom(array $array = [])
     {
         if (isset($this->config['rootElement'])) {
             $rootElement = $this->config['rootElement'];
-        } elseif (count($array) == 1) {
+        } elseif (1 == count($array)) {
             $rootElement = array_keys($array)[0];
             $array       = $array[$rootElement];
         } else {
@@ -122,7 +119,7 @@ public function convertFrom(array $array = [])
     /**
      * Return as XML.
      *
-     * @param  $prettyOutput  Format output for DOMDocument
+     * @param $prettyOutput Format output for DOMDocument
      *
      * @return string
      */
@@ -144,14 +141,14 @@ public function toDom()
     }
 
     /**
-     * Build XML node
+     * Build XML node.
      *
-     * @param  string $nodeName The name of the node that the data will be stored under
-     * @param  mixed  $data     The value to be build
+     * @param string $nodeName The name of the node that the data will be stored under
+     * @param mixed  $data     The value to be build
      *
      * @throws DOMException
      *
-     * @return DOMElement       The XML representation of the input data
+     * @return DOMElement The XML representation of the input data
      */
     protected function buildNode($nodeName, $data)
     {
@@ -162,7 +159,7 @@ protected function buildNode($nodeName, $data)
         $node = $this->xml->createElement($nodeName);
 
         if (is_array($data)) {
-            $this->parseArray($node, $nodeName, $data);
+            $this->parseArray($node, $data);
         } else {
             $node->appendChild($this->xml->createTextNode($this->normalizeValues($data)));
         }
@@ -171,20 +168,19 @@ protected function buildNode($nodeName, $data)
     }
 
     /**
-     * Parse array to build node
+     * Parse array to build node.
      *
-     * @param  DOMElement $node
-     * @param  string     $nodeName
-     * @param  array      $array
+     * @param DOMElement $node
+     * @param array      $array
      *
      * @throws DOMException
      *
      * @return void
      */
-    protected function parseArray(DOMElement $node, $nodeName, array $array)
+    protected function parseArray(DOMElement $node, array $array)
     {
         // get the attributes first.;
-        $array = $this->parseAttributes($node, $nodeName, $array);
+        $array = $this->parseAttributes($node, $array);
 
         // get value stored in @value
         $array = $this->parseValue($node, $array);
@@ -215,17 +211,16 @@ protected function parseArray(DOMElement $node, $nodeName, array $array)
     }
 
     /**
-     * Build attributes of node
+     * Build attributes of node.
      *
-     * @param  DOMElement $node
-     * @param  string     $nodeName
-     * @param  array      $array
+     * @param DOMElement $node
+     * @param array      $array
      *
      * @throws DOMException
      *
      * @return array
      */
-    protected function parseAttributes(DOMElement $node, $nodeName, array $array)
+    protected function parseAttributes(DOMElement $node, array $array)
     {
         $attributesKey = $this->config['attributesKey'];
 
@@ -245,12 +240,12 @@ protected function parseAttributes(DOMElement $node, $nodeName, array $array)
     }
 
     /**
-     * Build value of node
+     * Build value of node.
      *
-     * @param  DOMElement $node
-     * @param  array      $array
+     * @param DOMElement $node
+     * @param array      $array
      *
-     * @return DOMElement|array
+     * @return array
      */
     protected function parseValue(DOMElement $node, array $array)
     {
@@ -266,12 +261,12 @@ protected function parseValue(DOMElement $node, array $array)
     }
 
     /**
-     * Build CDATA of node
+     * Build CDATA of node.
      *
-     * @param  DOMElement $node
-     * @param  array      $array
+     * @param DOMElement $node
+     * @param array      $array
      *
-     * @return DOMElement|array
+     * @return array
      */
     protected function parseCdata(DOMElement $node, array $array)
     {
@@ -287,35 +282,35 @@ protected function parseCdata(DOMElement $node, array $array)
     }
 
     /**
-     * Get string representation of values
+     * Get string representation of values.
      *
-     * @param  mixed $value
+     * @param mixed $value
      *
      * @return string
      */
     protected function normalizeValues($value)
     {
-        $value = $value === true ? 'true' : $value;
-        $value = $value === false ? 'false' : $value;
-        $value = $value === null ? '' : $value;
+        $value = true  === $value ? 'true' : $value;
+        $value = false === $value ? 'false' : $value;
+        $value = null  === $value ? '' : $value;
 
         return (string) $value;
     }
 
     /**
-     * Check if the tag name or attribute name contains illegal characters
+     * Check if the tag name or attribute name contains illegal characters.
+     *
      * @see: http://www.w3.org/TR/xml/#sec-common-syn
      *
      * @param  string
+     * @param mixed $tag
      *
-     * @return boolean
+     * @return bool
      */
     protected function isValidTagName($tag)
     {
         $pattern = '/^[a-zA-Z_][\w\:\-\.]*$/';
 
-        return preg_match($pattern, $tag, $matches) && $matches[0] == $tag && substr($tag, -1, 1) != ':';
+        return preg_match($pattern, $tag, $matches) && $matches[0] == $tag && ':' != substr($tag, -1, 1);
     }
-
 }
-
diff --git a/src/Xml2Array.php b/src/Xml2Array.php
index ce36f25..bc2ed83 100644
--- a/src/Xml2Array.php
+++ b/src/Xml2Array.php
@@ -1,4 +1,6 @@
-<?php namespace Jackiedo\XmlArray;
+<?php
+
+namespace Jackiedo\XmlArray;
 
 use DOMDocument;
 use DOMException;
@@ -6,62 +8,56 @@
 use SimpleXMLElement;
 
 /**
- * Xml2Array: A class to convert XML to an array in PHP
+ * A class to convert XML to an array in PHP.
  * Takes a DOMDocument object or SimpleXMLElement object or an XML string as input.
  *
- * Usage:
- *       $array = Xml2Array::convert($xml)->toArray();
- *       $array = Xml2Array::convert($xml, ['useNamespaces' => true])->toArray();
- *       $json  = Xml2Array::convert($xml)->toJson();
+ * @see https://github.com/JackieDo/Xml-Array/blob/master/README.md Documentation.
  *
- * @package xml-array
  * @author Jackie Do <anhvudo@gmail.com>
- * @copyright 2018
- * @version $Id$
- * @access public
+ * @license MIT
  */
 class Xml2Array
 {
     /**
-     * The name of the XML attribute that indicates a namespace definition
+     * The name of the XML attribute that indicates a namespace definition.
      */
-    const ATTRIBUTE_NAMESPACE = 'xmlns';
+    public const ATTRIBUTE_NAMESPACE = 'xmlns';
 
     /**
-     * The string that separates the namespace attribute from the prefix for the namespace
+     * The string that separates the namespace attribute from the prefix for the namespace.
      */
-    const ATTRIBUTE_NAMESPACE_SEPARATOR = ':';
+    public const ATTRIBUTE_NAMESPACE_SEPARATOR = ':';
 
     /**
-     * The configuration of the current instance
+     * The configuration of the current instance.
      *
      * @var array
      */
     protected $config = [];
 
     /**
-     * The working XML document
+     * The working XML document.
      *
      * @var DOMDocument
      */
-    protected $xml = null;
+    protected $xml;
 
     /**
-     * The working list of XML namespaces
+     * The working list of XML namespaces.
      *
      * @var array
      */
     protected $namespaces = [];
 
     /**
-     * The result of this conversion
+     * The result of this conversion.
      *
      * @var array
      */
     protected $array = [];
 
     /**
-     * Constructor
+     * Constructor.
      *
      * @param array $config The configuration to use for this instance
      */
@@ -71,9 +67,9 @@ public function __construct(array $config = [])
     }
 
     /**
-     * Set configuration for converter
+     * Set configuration for converter.
      *
-     * @param  array  $config The configuration to use for conversion
+     * @param array $config The configuration to use for conversion
      *
      * @return $this
      */
@@ -85,7 +81,7 @@ public function setConfig(array $config = [])
             'attributesKey'    => '@attributes',
             'cdataKey'         => '@cdata',
             'valueKey'         => '@value',
-            'namespacesOnRoot' => true
+            'namespacesOnRoot' => true,
         ];
 
         $this->config = array_merge($defaultConfig, $config);
@@ -94,7 +90,7 @@ public function setConfig(array $config = [])
     }
 
     /**
-     * Return configuration of converter
+     * Return configuration of converter.
      *
      * @return array
      */
@@ -105,12 +101,12 @@ public function getConfig()
 
     /**
      * Convert an XML DOMDocument or XML string to an array
-     * A static facade for ease of use and backwards compatibility
+     * A static facade for ease of use and backwards compatibility.
      *
-     * @param  DOMDocument|SimpleXMLElement|string $xml      The XML to convert to an array
-     * @param  array                               $config   The configuration to use for the conversion
+     * @param DOMDocument|SimpleXMLElement|string $xml    The XML to convert to an array
+     * @param array                               $config The configuration to use for the conversion
      *
-     * @return array  An array representation of the input XML
+     * @return array An array representation of the input XML
      */
     public static function convert($xml, array $config = [])
     {
@@ -120,11 +116,11 @@ public static function convert($xml, array $config = [])
     }
 
     /**
-     * Convert input XML to an array
+     * Convert input XML to an array.
      *
-     * @param  DOMDocument|SimpleXMLElement|string $inputXml The XML to convert to an array
+     * @param DOMDocument|SimpleXMLElement|string $inputXml The XML to convert to an array
      *
-     * @return array  An array representation of the input XML
+     * @return array An array representation of the input XML
      */
     public function convertFrom($inputXml)
     {
@@ -156,7 +152,7 @@ public function convertFrom($inputXml)
     }
 
     /**
-     * Export result as array
+     * Export result as array.
      *
      * @return array
      */
@@ -166,21 +162,21 @@ public function toArray()
     }
 
     /**
-     * Get result as json string
+     * Get result as json string.
      *
-     * @param  integer $options
+     * @param int $flags
      *
      * @return string
      */
-    public function toJson($options = 0)
+    public function toJson($flags = 0)
     {
-        return json_encode($this->array, $options);
+        return json_encode($this->array, $flags);
     }
 
     /**
-     * Load input into DOMDocument
+     * Load input into DOMDocument.
      *
-     * @param  DOMDocument|SimpleXMLElement|string $inputXml The XML to convert to an array
+     * @param DOMDocument|SimpleXMLElement|string $inputXml The XML to convert to an array
      *
      * @throws DOMException
      *
@@ -193,7 +189,7 @@ protected function loadXml($inputXml)
         if (is_string($inputXml)) {
             $parse = @$this->xml->loadXML($inputXml);
 
-            if ($parse === false) {
+            if (false === $parse) {
                 throw new DOMException('Error parsing XML string, input is not a well-formed XML string.');
             }
         } elseif ($inputXml instanceof SimpleXMLElement) {
@@ -206,9 +202,9 @@ protected function loadXml($inputXml)
     }
 
     /**
-     * Parse an XML DOMNode
+     * Parse an XML DOMNode.
      *
-     * @param  DOMNode $node A single XML DOMNode
+     * @param DOMNode $node A single XML DOMNode
      *
      * @return mixed
      */
@@ -237,17 +233,17 @@ protected function parseNode(DOMNode $node)
     }
 
     /**
-     * Parse child nodes of DOMNode
+     * Parse child nodes of DOMNode.
      *
-     * @param  DOMNode $node
-     * @param  mixed   $output
+     * @param DOMNode $node
+     * @param mixed   $output
      *
      * @return mxied
      */
     protected function parseChildNodes(DOMNode $node, $output)
     {
         foreach ($node->childNodes as $child) {
-            if ($child->nodeType === XML_CDATA_SECTION_NODE) {
+            if (XML_CDATA_SECTION_NODE === $child->nodeType) {
                 if (!is_array($output)) {
                     if (!empty($output)) {
                         $output = [$this->config['valueKey'] => $output];
@@ -260,15 +256,15 @@ protected function parseChildNodes(DOMNode $node, $output)
             } else {
                 $value = $this->parseNode($child);
 
-                if ($child->nodeType == XML_TEXT_NODE) {
-                    if ($value != '') {
+                if (XML_TEXT_NODE == $child->nodeType) {
+                    if ('' != $value) {
                         if (!empty($output)) {
                             $output[$this->config['valueKey']] = $value;
                         } else {
                             $output = $value;
                         }
                     }
-                } elseif ($child->nodeType !== XML_COMMENT_NODE) {
+                } elseif (XML_COMMENT_NODE !== $child->nodeType) {
                     $nodeName = $child->nodeName;
 
                     if (!isset($output[$nodeName])) {
@@ -284,9 +280,9 @@ protected function parseChildNodes(DOMNode $node, $output)
     }
 
     /**
-     * Clean text content of text node
+     * Clean text content of text node.
      *
-     * @param  string $textContent
+     * @param string $textContent
      *
      * @return string
      */
@@ -296,14 +292,14 @@ protected function normalizeTextContent($textContent)
             '/\n+\s+/',
             '/\r+\s+/',
             '/\n+\t+/',
-            '/\r+\t+/'
+            '/\r+\t+/',
         ], ' ', $textContent));
     }
 
     /**
-     * Normalize values of node
+     * Normalize values of node.
      *
-     * @param  mixed $values
+     * @param mixed $values
      *
      * @return mixed
      */
@@ -312,7 +308,7 @@ protected function normalizeNodeValues($values)
         if (is_array($values)) {
             // if only one node of its kind, assign it directly instead if array($value);
             foreach ($values as $key => $value) {
-                if (is_array($value) && count($value) === 1) {
+                if (is_array($value) && 1 === count($value)) {
                     $keyName = array_keys($value)[0];
 
                     if (is_numeric($keyName)) {
@@ -330,10 +326,10 @@ protected function normalizeNodeValues($values)
     }
 
     /**
-     * Parse DOMNode to get its attributes
+     * Parse DOMNode to get its attributes.
      *
-     * @param  DOMNode $node
-     * @param  mixed   $output
+     * @param DOMNode $node
+     * @param mixed   $output
      *
      * @return mixed
      */
@@ -375,10 +371,10 @@ protected function collectAttributes(DOMNode $node, $output)
     }
 
     /**
-     * Collect namespaces for special DOMNode
+     * Collect namespaces for special DOMNode.
      *
-     * @param  DOMNode $node
-     * @param  array   $output
+     * @param DOMNode $node
+     * @param array   $output
      *
      * @return array
      */
@@ -394,9 +390,9 @@ protected function collectNodeNamespaces(DOMNode $node, array $output)
     }
 
     /**
-     * Get the namespace of the supplied node, and add it to the list of known namespaces for this document
+     * Get the namespace of the supplied node, and add it to the list of known namespaces for this document.
      *
-     * @param  DOMNode $node
+     * @param DOMNode $node
      *
      * @return mixed
      */
diff --git a/tests/.gitkeep b/tests/.gitkeep
deleted file mode 100644
index e69de29..0000000
diff --git a/tests/Array2XmlTest.php b/tests/Array2XmlTest.php
index eb487b0..136a245 100644
--- a/tests/Array2XmlTest.php
+++ b/tests/Array2XmlTest.php
@@ -3,67 +3,70 @@
 use Jackiedo\XmlArray\Array2Xml;
 use PHPUnit\Framework\TestCase;
 
+/**
+ * @internal
+ * @coversNothing
+ */
 class Array2XmlTest extends TestCase
 {
     /**
-     * Input for test
+     * Input for test.
      *
      * @var array
      */
     protected $input_array = [
-        "root_node" => [
-            "tag" => "Example tag",
-            "attribute_tag" => [
-                "@value" => "Another tag with attributes",
-                "@attributes" => [
-                    "description" => "This is a tag with attribute"
-                ]
+        'root_node' => [
+            'tag'           => 'Example tag',
+            'attribute_tag' => [
+                '@value'      => 'Another tag with attributes',
+                '@attributes' => [
+                    'description' => 'This is a tag with attribute',
+                ],
             ],
-            "cdata_section" => [
-                "@cdata" => "This is CDATA section"
+            'cdata_section' => [
+                '@cdata' => 'This is CDATA section',
             ],
-            "tag_with_subtag" => [
-                "sub_tag" => ["Sub tag 1", "Sub tag 2"]
+            'tag_with_subtag' => [
+                'sub_tag' => ['Sub tag 1', 'Sub tag 2'],
             ],
-            "mixed_section" => [
-                "@value" => "Hello",
-                "@cdata" => "This is another CDATA section",
-                "section" => [
+            'mixed_section' => [
+                '@value'  => 'Hello',
+                '@cdata'  => 'This is another CDATA section',
+                'section' => [
                     [
-                        "@value" => "Section number 1",
-                        "@attributes" => [
-                            "id" => "sec_1"
-                        ]
+                        '@value'      => 'Section number 1',
+                        '@attributes' => [
+                            'id' => 'sec_1',
+                        ],
                     ],
                     [
-                        "@value" => "Section number 2",
-                        "@attributes" => [
-                            "id" => "sec_2"
-                        ]
+                        '@value'      => 'Section number 2',
+                        '@attributes' => [
+                            'id' => 'sec_2',
+                        ],
                     ],
                     [
-                        "@value" => "Section number 3",
-                        "@attributes" => [
-                            "id" => "sec_3"
-                        ]
-                    ]
-                ]
+                        '@value'      => 'Section number 3',
+                        '@attributes' => [
+                            'id' => 'sec_3',
+                        ],
+                    ],
+                ],
             ],
-            "example:with_namespace" => [
-                "@attributes" => [
-                    "xmlns:example" => "http://example.com"
+            'example:with_namespace' => [
+                '@attributes' => [
+                    'xmlns:example' => 'http://example.com',
                 ],
-                "example:sub" => "Content"
+                'example:sub' => 'Content',
             ],
-        ]
+        ],
     ];
 
     /**
-     * Throw DOMException when there are more than one root node
+     * Throw DOMException when there are more than one root node.
      *
+     * @testdox Throw DOMException when there are more than one root node.
      * @test
-     *
-     * @return void
      */
     public function throw_dom_exception_when_there_are_more_than_one_root_node()
     {
@@ -71,17 +74,16 @@ public function throw_dom_exception_when_there_are_more_than_one_root_node()
         $this->expectExceptionMessage('XML documents are allowed only one root element. Wrap your elements in a key or set the `rootElement` parameter in the configuration.');
 
         $process = Array2Xml::convert([
-            'root' => 'content',
-            'another_root' => 'Another content'
+            'root'         => 'content',
+            'another_root' => 'Another content',
         ]);
     }
 
     /**
-     * Throw DOMException when node name is invalid
+     * Throw DOMException when node name is invalid.
      *
+     * @testdox Throw DOMException when node name is invalid.
      * @test
-     *
-     * @return void
      */
     public function throw_dom_exception_when_node_name_is_invalid()
     {
@@ -92,11 +94,10 @@ public function throw_dom_exception_when_node_name_is_invalid()
     }
 
     /**
-     * Throw DOMException when attribute name is invalid
+     * Throw DOMException when attribute name is invalid.
      *
+     * @testdox Throw DOMException when attribute name is invalid.
      * @test
-     *
-     * @return void
      */
     public function throw_dom_exception_when_attaribute_name_is_invalid()
     {
@@ -107,19 +108,18 @@ public function throw_dom_exception_when_attaribute_name_is_invalid()
             'root' => [
                 'sub' => [
                     '@attributes' => [
-                        'invalid attribute' => 'Attribute value'
-                    ]
-                ]
-            ]
+                        'invalid attribute' => 'Attribute value',
+                    ],
+                ],
+            ],
         ]);
     }
 
     /**
-     * Convert array to XML string
+     * Convert array to XML string.
      *
+     * @testdox Convert array to XML string.
      * @test
-     *
-     * @return void
      */
     public function convert_array_to_xml_string()
     {
@@ -127,11 +127,10 @@ public function convert_array_to_xml_string()
     }
 
     /**
-     * Convert array to DOM
+     * Convert array to DOM.
      *
+     * @testdox Convert array to DOM.
      * @test
-     *
-     * @return void
      */
     public function convert_array_to_dom()
     {
diff --git a/tests/Xml2ArrayTest.php b/tests/Xml2ArrayTest.php
index ff62907..6909030 100644
--- a/tests/Xml2ArrayTest.php
+++ b/tests/Xml2ArrayTest.php
@@ -3,115 +3,115 @@
 use Jackiedo\XmlArray\Xml2Array;
 use PHPUnit\Framework\TestCase;
 
+/**
+ * @internal
+ * @coversNothing
+ */
 class Xml2ArrayTest extends TestCase
 {
     /**
-     * Store expected result for full test
+     * Store expected result for full test.
      *
      * @var string
      */
     protected $fulltest_expected_result = [
-        "root_node" => [
-            "tag" => "Example tag",
-            "attribute_tag" => [
-                "@value" => "Another tag with attributes",
-                "@attributes" => [
-                    "description" => "This is a tag with attribute"
-                ]
+        'root_node' => [
+            'tag'           => 'Example tag',
+            'attribute_tag' => [
+                '@value'      => 'Another tag with attributes',
+                '@attributes' => [
+                    'description' => 'This is a tag with attribute',
+                ],
             ],
-            "cdata_section" => [
-                "@cdata" => "This is CDATA section"
+            'cdata_section' => [
+                '@cdata' => 'This is CDATA section',
             ],
-            "tag_with_subtag" => [
-                "sub_tag" => ["Sub tag 1", "Sub tag 2"]
+            'tag_with_subtag' => [
+                'sub_tag' => ['Sub tag 1', 'Sub tag 2'],
             ],
-            "mixed_section" => [
-                "@value" => "Hello",
-                "@cdata" => "This is another CDATA section",
-                "section" => [
+            'mixed_section' => [
+                '@value'  => 'Hello',
+                '@cdata'  => 'This is another CDATA section',
+                'section' => [
                     [
-                        "@value" => "Section number 1",
-                        "@attributes" => [
-                            "id" => "sec_1"
-                        ]
+                        '@value'      => 'Section number 1',
+                        '@attributes' => [
+                            'id' => 'sec_1',
+                        ],
                     ],
                     [
-                        "@value" => "Section number 2",
-                        "@attributes" => [
-                            "id" => "sec_2"
-                        ]
+                        '@value'      => 'Section number 2',
+                        '@attributes' => [
+                            'id' => 'sec_2',
+                        ],
                     ],
                     [
-                        "@value" => "Section number 3",
-                        "@attributes" => [
-                            "id" => "sec_3"
-                        ]
-                    ]
-                ]
+                        '@value'      => 'Section number 3',
+                        '@attributes' => [
+                            'id' => 'sec_3',
+                        ],
+                    ],
+                ],
             ],
-            "example:with_namespace" => [
-                "@attributes" => [
-                    "xmlns:example" => "http://example.com"
+            'example:with_namespace' => [
+                '@attributes' => [
+                    'xmlns:example' => 'http://example.com',
                 ],
-                "example:sub" => "Content"
+                'example:sub' => 'Content',
             ],
-        ]
+        ],
     ];
 
     /**
-     * Convert to array from an XML string containing only one empty node
+     * Convert to array from an XML string containing only one empty node.
      *
+     * @testdox Convert to array from an XML string containing only one empty node.
      * @test
-     *
-     * @return void
      */
     public function convert_to_array_from_an_xml_string_containing_only_one_empty_node()
     {
         $string = '<root />';
 
         $this->assertEquals([
-            'root' => ''
+            'root' => '',
         ], Xml2Array::convert($string)->toArray());
     }
 
     /**
-     * Convert to array from an XML string containing one node with empty value
+     * Convert to array from an XML string containing one node with empty value.
      *
+     * @testdox Convert to array from an XML string containing one node with empty value.
      * @test
-     *
-     * @return void
      */
     public function convert_to_array_from_an_xml_string_containing_one_node_with_empty_value()
     {
         $string = '<root></root>';
 
         $this->assertEquals([
-            'root' => ''
+            'root' => '',
         ], Xml2Array::convert($string)->toArray());
     }
 
     /**
-     * Convert to array from XML string containing one node that whose value is on one line
+     * Convert to array from XML string containing one node that whose value is on one line.
      *
+     * @testdox Convert to array from XML string containing one node that whose value is on one line.
      * @test
-     *
-     * @return void
      */
     public function convert_to_array_from_xml_string_containing_one_node_that_whose_value_is_on_one_line()
     {
         $string = '<root>Welcome to Xml2Array Converter</root>';
 
         $this->assertEquals([
-            'root' => 'Welcome to Xml2Array Converter'
+            'root' => 'Welcome to Xml2Array Converter',
         ], Xml2Array::convert($string)->toArray());
     }
 
     /**
-     * Convert to array from XML string containing one node that whose value is on multilines
+     * Convert to array from XML string containing one node that whose value is on multilines.
      *
+     * @testdox Convert to array from XML string containing one node that whose value is on multilines.
      * @test
-     *
-     * @return void
      */
     public function convert_to_array_from_xml_string_containing_one_node_that_whose_value_is_on_multilines()
     {
@@ -123,16 +123,15 @@ public function convert_to_array_from_xml_string_containing_one_node_that_whose_
         </root>';
 
         $this->assertEquals([
-            'root' => "Welcome to Xml2Array Converter"
+            'root' => 'Welcome to Xml2Array Converter',
         ], Xml2Array::convert($string)->toArray());
     }
 
     /**
-     * Convert to array from XML string containing one node that whose value is Cdata Section
+     * Convert to array from XML string containing one node that whose value is Cdata Section.
      *
+     * @testdox Convert to array from XML string containing one node that whose value is Cdata Section.
      * @test
-     *
-     * @return void
      */
     public function convert_to_array_from_xml_string_containing_one_node_that_whose_value_is_cdata_section()
     {
@@ -140,17 +139,16 @@ public function convert_to_array_from_xml_string_containing_one_node_that_whose_
 
         $this->assertEquals([
             'root' => [
-                '@cdata' => 'This is CDATA section'
-            ]
+                '@cdata' => 'This is CDATA section',
+            ],
         ], Xml2Array::convert($string)->toArray());
     }
 
     /**
-     * Convert to array from XML string that root node has sub node
+     * Convert to array from XML string that root node has sub node.
      *
+     * @testdox Convert to array from XML string that root node has sub node.
      * @test
-     *
-     * @return void
      */
     public function convert_to_array_from_xml_string_that_root_node_has_sub_node()
     {
@@ -162,17 +160,16 @@ public function convert_to_array_from_xml_string_that_root_node_has_sub_node()
         $this->assertEquals([
             'root' => [
                 'subnode_1' => 'Node value',
-                'subnode_2' => 'Node value'
-            ]
+                'subnode_2' => 'Node value',
+            ],
         ], Xml2Array::convert($string)->toArray());
     }
 
     /**
-     * Convert to array from XML string that node only has attributes
+     * Convert to array from XML string that node only has attributes.
      *
+     * @testdox Convert to array from XML string that node only has attributes.
      * @test
-     *
-     * @return void
      */
     public function convert_to_array_from_xml_string_that_node_only_has_attributes()
     {
@@ -185,24 +182,23 @@ public function convert_to_array_from_xml_string_that_node_only_has_attributes()
             'root' => [
                 'subnode_1' => [
                     '@attributes' => [
-                        'description' => 'Subnode #1'
-                    ]
+                        'description' => 'Subnode #1',
+                    ],
                 ],
                 'subnode_2' => [
                     '@attributes' => [
-                        'description' => 'Subnode #2'
-                    ]
-                ]
-            ]
+                        'description' => 'Subnode #2',
+                    ],
+                ],
+            ],
         ], Xml2Array::convert($string)->toArray());
     }
 
     /**
-     * Convert to array from XML string that node has value and attributes
+     * Convert to array from XML string that node has value and attributes.
      *
+     * @testdox Convert to array from XML string that node has value and attributes.
      * @test
-     *
-     * @return void
      */
     public function convert_to_array_from_xml_string_that_node_has_value_and_attributes()
     {
@@ -214,27 +210,26 @@ public function convert_to_array_from_xml_string_that_node_has_value_and_attribu
         $this->assertEquals([
             'root' => [
                 'subnode_1' => [
-                    '@value' => 'Node value',
+                    '@value'      => 'Node value',
                     '@attributes' => [
-                        'description' => 'Subnode #1'
-                    ]
+                        'description' => 'Subnode #1',
+                    ],
                 ],
                 'subnode_2' => [
-                    '@value' => 'Node value',
+                    '@value'      => 'Node value',
                     '@attributes' => [
-                        'description' => 'Subnode #2'
-                    ]
-                ]
-            ]
+                        'description' => 'Subnode #2',
+                    ],
+                ],
+            ],
         ], Xml2Array::convert($string)->toArray());
     }
 
     /**
-     * Convert to array from XML string containing has namespaces
+     * Convert to array from XML string containing has namespaces.
      *
+     * @testdox Convert to array from XML string containing has namespaces.
      * @test
-     *
-     * @return void
      */
     public function convert_to_array_from_xml_string_containing_has_namespaces()
     {
@@ -249,25 +244,24 @@ public function convert_to_array_from_xml_string_containing_has_namespaces()
             'root_node' => [
                 'example:node_with_namespace' => [
                     'example:sub' => [
-                        '@value' => 'Content',
+                        '@value'      => 'Content',
                         '@attributes' => [
-                            'example:description' => 'An attribute with namespace'
-                        ]
-                    ]
+                            'example:description' => 'An attribute with namespace',
+                        ],
+                    ],
                 ],
                 '@attributes' => [
-                    'xmlns:example' => 'http://example.com'
-                ]
-            ]
+                    'xmlns:example' => 'http://example.com',
+                ],
+            ],
         ], Xml2Array::convert($string)->toArray());
     }
 
     /**
-     * Convert to array from XML string with special config
+     * Convert to array from XML string with special config.
      *
+     * @testdox Convert to array from XML string with special config.
      * @test
-     *
-     * @return void
      */
     public function convert_to_array_from_xml_string_with_special_config()
     {
@@ -279,21 +273,22 @@ public function convert_to_array_from_xml_string_with_special_config()
         $this->assertEquals([
             'root_node' => [
                 'sub_node' => [
-                    '#text' => 'Content',
+                    '#text'       => 'Content',
                     '#attributes' => [
-                        'description' => 'An attribute'
-                    ]
-                ]
-            ]
+                        'description' => 'An attribute',
+                    ],
+                ],
+            ],
         ], Xml2Array::convert($string, [
-            'valueKey' => '#text',
-            'attributesKey' => '#attributes'
+            'valueKey'      => '#text',
+            'attributesKey' => '#attributes',
         ])->toArray());
     }
 
     /**
-     * Convert from XML string to array with all cases
+     * Convert from XML string to array with all cases.
      *
+     * @testdox Convert from XML string to array with all cases.
      * @test
      */
     public function convert_from_xml_string_to_array_with_all_cases()
@@ -301,15 +296,16 @@ public function convert_from_xml_string_to_array_with_all_cases()
         $string = file_get_contents(__DIR__ . '/resources/example.xml');
 
         $result = Xml2Array::convert($string, [
-            'namespacesOnRoot' => false
+            'namespacesOnRoot' => false,
         ])->toArray();
 
         $this->assertEquals($this->fulltest_expected_result, $result);
     }
 
     /**
-     * Convert from XML object to array with all cases
+     * Convert from XML object to array with all cases.
      *
+     * @testdox Convert from XML object to array with all cases.
      * @test
      */
     public function convert_from_xml_object_to_array()
@@ -317,15 +313,16 @@ public function convert_from_xml_object_to_array()
         $xmlObject = simplexml_load_file(__DIR__ . '/resources/example.xml');
 
         $result = Xml2Array::convert($xmlObject, [
-            'namespacesOnRoot' => false
+            'namespacesOnRoot' => false,
         ])->toArray();
 
         $this->assertEquals($this->fulltest_expected_result, $result);
     }
 
     /**
-     * Convert from DOM object to array with all cases
+     * Convert from DOM object to array with all cases.
      *
+     * @testdox Convert from DOM object to array with all cases.
      * @test
      */
     public function convert_from_dom_object_to_array()
@@ -334,18 +331,17 @@ public function convert_from_dom_object_to_array()
         $domObject->load(__DIR__ . '/resources/example.xml');
 
         $result = Xml2Array::convert($domObject, [
-            'namespacesOnRoot' => false
+            'namespacesOnRoot' => false,
         ])->toArray();
 
         $this->assertEquals($this->fulltest_expected_result, $result);
     }
 
     /**
-     * Throw DOMException when input XML string is not well-formed XML
+     * Throw DOMException when input XML string is not well-formed XML.
      *
+     * @testdox Throw DOMException when input XML string is not well-formed XML.
      * @test
-     *
-     * @return void
      */
     public function throw_dom_exception_when_input_xml_string_not_well_formed()
     {
@@ -356,11 +352,10 @@ public function throw_dom_exception_when_input_xml_string_not_well_formed()
     }
 
     /**
-     * Throw DOMException when invalid input
+     * Throw DOMException when invalid input.
      *
+     * @testdox Throw DOMException when invalid input.
      * @test
-     *
-     * @return void
      */
     public function throw_dom_exception_when_invalid_input()
     {
@@ -371,8 +366,9 @@ public function throw_dom_exception_when_invalid_input()
     }
 
     /**
-     * Convert from XML string to Json
+     * Convert from XML string to Json.
      *
+     * @testdox Convert from XML string to Json.
      * @test
      */
     public function convert_from_xml_string_to_json()