diff --git a/src/ScriptHandler.php b/src/ScriptHandler.php
index 29b8b7f..732cc59 100644
--- a/src/ScriptHandler.php
+++ b/src/ScriptHandler.php
@@ -18,11 +18,13 @@ class ScriptHandler
     const OPTION_KEY_FORMATTER     = 'format';
     const DEFAULT_OPTION_FORMATTER = 'compact';
     protected static $mandatoryOptions = [
-        self::OPTION_KEY_INPUT,
-        self::OPTION_KEY_OUTPUT
+        self::OPTION_KEY_INPUT  => 'array',
+        self::OPTION_KEY_OUTPUT => 'string'
     ];
 
     /**
+     * @api
+     *
      * @param Event $event
      *
      * @throws \InvalidArgumentException
@@ -34,20 +36,26 @@ public static function generateCSS(Event $event)
 
         $processor = new Processor($event->getIO());
 
-        foreach ($extra[static::CONFIG_MAIN_KEY] as $config) {
-            foreach ($config[static::OPTION_KEY_INPUT] as $inputSource) {
+        foreach ($extra[static::CONFIG_MAIN_KEY] as $options) {
+            foreach ($options[static::OPTION_KEY_INPUT] as $inputSource) {
                 $processor->attachFiles(
                     static::resolvePath($inputSource, getcwd()),
-                    static::resolvePath($config[static::OPTION_KEY_OUTPUT], getcwd())
+                    static::resolvePath($options[static::OPTION_KEY_OUTPUT], getcwd())
                 );
             }
 
-            $formatter = isset($config[static::OPTION_KEY_FORMATTER]) ? $config[static::OPTION_KEY_FORMATTER] : static::DEFAULT_OPTION_FORMATTER;
+            $formatter = array_key_exists(static::OPTION_KEY_FORMATTER, $options) ? $options[static::OPTION_KEY_FORMATTER] : static::DEFAULT_OPTION_FORMATTER;
             $processor->processFiles($formatter);
         }
         $processor->saveOutput();
     }
 
+    /**
+     * @param string $path
+     * @param string $prefix
+     *
+     * @return string
+     */
     protected static function resolvePath($path, $prefix)
     {
         return '/' === substr($path, 0, 1) ? $path : "{$prefix}/{$path}";
@@ -56,92 +64,44 @@ protected static function resolvePath($path, $prefix)
     /**
      * @param array $config
      *
-     * @return bool
      * @throws \InvalidArgumentException
      */
     protected static function validateConfiguration(array $config)
     {
-        if (empty($config[static::CONFIG_MAIN_KEY])) {
+        if (!array_key_exists(static::CONFIG_MAIN_KEY, $config)) {
             throw new \InvalidArgumentException('compiler should needs to be configured through the extra.css-compiler setting');
         }
 
         if (!is_array($config[static::CONFIG_MAIN_KEY])) {
-            throw new \InvalidArgumentException('the extra.css-compiler setting must be an array of objects');
+            throw new \InvalidArgumentException('the extra.' . static::CONFIG_MAIN_KEY . ' setting must be an array of objects');
         }
 
-        return static::validateOptions($config[static::CONFIG_MAIN_KEY]);
-    }
-
-    /**
-     * @param array $config
-     *
-     * @return bool
-     * @throws \InvalidArgumentException
-     */
-    protected static function validateOptions(array $config)
-    {
-        foreach ($config as $option) {
-            if (!is_array($option)) {
-                throw new \InvalidArgumentException('extra.' . static::CONFIG_MAIN_KEY . "[]." . static::OPTION_KEY_INPUT . ' array');
+        foreach ($config[static::CONFIG_MAIN_KEY] as $index => $options) {
+            if (!is_array($options)) {
+                throw new \InvalidArgumentException('extra.' . static::CONFIG_MAIN_KEY . "[$index] should be an array");
             }
 
-            static::validateMandatoryOptions($option);
+            static::validateMandatoryOptions($options, $index);
         }
-
-        return true;
     }
 
     /**
-     * @param array $config
+     * @param array $options
+     * @param int   $index
      *
-     * @return bool
      * @throws \InvalidArgumentException
      */
-    protected static function validateMandatoryOptions(array $config)
+    protected static function validateMandatoryOptions(array $options, $index)
     {
-        foreach (static::$mandatoryOptions as $option) {
-            if (empty($config[$option])) {
-                throw new \InvalidArgumentException('extra.' . static::CONFIG_MAIN_KEY . "[].{$option} is required!");
+        foreach (static::$mandatoryOptions as $optionIndex => $type) {
+            if (!array_key_exists($optionIndex, $options)) {
+                throw new \InvalidArgumentException('extra.' . static::CONFIG_MAIN_KEY . "[$index].{$optionIndex} is required!");
             }
 
-            switch ($option) {
-                case static::OPTION_KEY_INPUT:
-                    static::validateIsArray($config[$option]);
-                    break;
-                case static::OPTION_KEY_OUTPUT:
-                    static::validateIsString($config[$option]);
-                    break;
+            $callable = "is_{$type}";
+            if (!$callable($options[$optionIndex])) {
+                throw new \InvalidArgumentException('extra.' . static::CONFIG_MAIN_KEY . "[$index].{$optionIndex} should be {$type}!");
             }
         }
-
-        return true;
-    }
-
-    /**
-     * @param array $option
-     *
-     * @return bool
-     */
-    protected static function validateIsArray($option)
-    {
-        if (!is_array($option)) {
-            throw new \InvalidArgumentException('extra.' . static::CONFIG_MAIN_KEY . '[]' . static::OPTION_KEY_INPUT . ' should be array!');
-        }
-
-        return true;
-    }
-
-    /**
-     * @param string $option
-     *
-     * @return bool
-     */
-    protected static function validateIsString($option)
-    {
-        if (!is_string($option)) {
-            throw new \InvalidArgumentException('extra.' . static::CONFIG_MAIN_KEY . '[]' . static::OPTION_KEY_OUTPUT . ' should string!');
-        }
-
-        return true;
     }
 }
diff --git a/tests/phpunit/ScriptHandlerTest.php b/tests/phpunit/ScriptHandlerTest.php
index 83fdd80..3ba63c4 100644
--- a/tests/phpunit/ScriptHandlerTest.php
+++ b/tests/phpunit/ScriptHandlerTest.php
@@ -72,88 +72,101 @@ public function validateConfigurationOnValid()
             ]
         ];
 
-        $this->assertTrue($this->validateConfiguration($args));
+        $this->assertNull($this->validateConfiguration($args));
     }
 
+    /**
+     * @see ScriptHandler::validateConfiguration
+     *
+     * @param $args
+     *
+     * @return bool
+     */
     private function validateConfiguration($args)
     {
         return $this->invokeMethod(new ScriptHandler(), 'validateConfiguration', [$args]);
     }
     /*** *************************** OPTIONS VALIDATION *************************** ***/
     /**
-     * @see ScriptHandler::validateOptions
+     * @see ScriptHandler::validateMandatoryOptions
      * @test
      *
      * @expectedException \InvalidArgumentException
      */
     public function validateOptionsExpectedExceptionOnMissingInput()
     {
-        $this->validateOptions([[ScriptHandler::OPTION_KEY_OUTPUT => 'output']]);
+        $this->validateMandatoryOptions([[ScriptHandler::OPTION_KEY_OUTPUT => 'output']]);
     }
 
     /**
-     * @see ScriptHandler::validateOptions
+     * @see ScriptHandler::validateMandatoryOptions
      * @test
      *
      * @expectedException \InvalidArgumentException
      */
     public function validateOptionsExpectedExceptionOnMissingOutput()
     {
-        $this->validateOptions([ScriptHandler::OPTION_KEY_INPUT => 'input']);
+        $this->validateMandatoryOptions([ScriptHandler::OPTION_KEY_INPUT => 'input']);
     }
 
     /**
-     * @see ScriptHandler::validateOptions
+     * @see ScriptHandler::validateMandatoryOptions
      * @test
      *
      * @expectedException \InvalidArgumentException
      */
     public function validateOptionsExpectedExceptionOnInputNotArray()
     {
-        $this->validateOptions([
+        $this->validateMandatoryOptions([
             ScriptHandler::OPTION_KEY_INPUT  => 'string',
             ScriptHandler::OPTION_KEY_OUTPUT => 'string'
         ]);
     }
 
     /**
-     * @see ScriptHandler::validateOptions
+     * @see ScriptHandler::validateMandatoryOptions
      * @test
      *
      * @expectedException \InvalidArgumentException
      */
     public function validateOptionsExpectedExceptionOnOutputNotString()
     {
-        $this->validateOptions([
+        $this->validateMandatoryOptions([
             ScriptHandler::OPTION_KEY_INPUT  => ['string'],
             ScriptHandler::OPTION_KEY_OUTPUT => ['string']
         ]);
     }
 
     /**
-     * @see ScriptHandler::validateOptions
+     * @see   ScriptHandler::validateMandatoryOptions
      * @test
+     *
+     * @group tester
      */
     public function validateOptionsOnValid()
     {
-        $this->assertTrue(
-            $this->validateOptions([
-                ScriptHandler::OPTION_KEY_INPUT  => ['string'],
-                ScriptHandler::OPTION_KEY_OUTPUT => 'string'
-            ])
+        $this->assertNull(
+            $this->validateMandatoryOptions(
+                [
+                    ScriptHandler::OPTION_KEY_INPUT  => ['string'],
+                    ScriptHandler::OPTION_KEY_OUTPUT => 'string'
+                ]
+            )
         );
     }
 
     /**
+     * @see ScriptHandler::validateMandatoryOptions
+     *
      * @param array $config
      *
      * @return bool
      */
-    private function validateOptions($config)
+    private function validateMandatoryOptions($config)
     {
-        return $this->invokeMethod(new ScriptHandler(), 'validateOptions', [[$config]]);
+        return $this->invokeMethod(new ScriptHandler(), 'validateMandatoryOptions', [$config, 1]);
     }
-    
+
     /*** *************************** INTEGRATION *************************** ***/
     /**
      * @see   ScriptHandler::generateCSS