Fix some mistakes

As mentioned in #6: we can't use Assert in production code.
Also, the Behat scenarios didn't pass

Author: matthiasnoback

features/interactive.feature

@@ -64,9 +64,9 @@ Feature: It is possible to interactively fill in a form from the CLI
     And the output should be
     """
       Select color [red]:
-        [0] Red
-        [1] Blue
-        [2] Yellow
+        [0] Red (red)
+        [1] Blue (blue)
+        [2] Yellow (yellow)
       > Array
       (
           [color] => blue
@@ -83,9 +83,9 @@ Feature: It is possible to interactively fill in a form from the CLI
     And the output should be
     """
       Select color [red]:
-        [0] Red
-        [1] Blue
-        [2] Yellow
+        [0] Red (red)
+        [1] Blue (blue)
+        [2] Yellow (yellow)
       > Array
       (
           [color] => red

src/Console/Helper/Question/AlwaysReturnKeyOfChoiceQuestion.php

@@ -17,12 +17,7 @@ class AlwaysReturnKeyOfChoiceQuestion extends ChoiceQuestion
 
     public function __construct($question, array $choiceViews, $default = null)
     {
-        \Assert\that($choiceViews)
-            ->all()
-            ->isInstanceOf(
-                'Symfony\Component\Form\Extension\Core\View\ChoiceView',
-                'Only a flat choice hierarchy is supported'
-            );
+        $this->assertFlatChoiceViewsArray($choiceViews);
 
         $this->choiceViews = $choiceViews;
 
@@ -117,4 +112,13 @@ private function prepareAutocompleteValues()
 
         return $autocompleteValues;
     }
+
+    private function assertFlatChoiceViewsArray(array $choiceViews)
+    {
+        foreach ($choiceViews as $choiceView) {
+            if (!$choiceView instanceof ChoiceView) {
+                throw new \InvalidArgumentException('Only a flat choice hierarchy is supported');
+            }
+        }
+    }
 }