Better message for Length rule

Update exception message when minimum value and maximum value are the
same.

library/Exceptions/LengthException.php

@@ -16,17 +16,20 @@ class LengthException extends ValidationException
     const BOTH = 0;
     const LOWER = 1;
     const GREATER = 2;
+    const EXACT = 3;
 
     public static $defaultTemplates = [
         self::MODE_DEFAULT => [
             self::BOTH => '{{name}} must have a length between {{minValue}} and {{maxValue}}',
             self::LOWER => '{{name}} must have a length greater than {{minValue}}',
             self::GREATER => '{{name}} must have a length lower than {{maxValue}}',
+            self::EXACT => '{{name}} must have a length of {{maxValue}}',
         ],
         self::MODE_NEGATIVE => [
             self::BOTH => '{{name}} must not have a length between {{minValue}} and {{maxValue}}',
             self::LOWER => '{{name}} must not have a length greater than {{minValue}}',
             self::GREATER => '{{name}} must not have a length lower than {{maxValue}}',
+            self::EXACT => '{{name}} must not have a length of {{maxValue}}',
         ],
     ];
 
@@ -34,10 +37,16 @@ class LengthException extends ValidationException
     {
         if (!$this->getParam('minValue')) {
             return static::GREATER;
-        } elseif (!$this->getParam('maxValue')) {
+        }
+
+        if (!$this->getParam('maxValue')) {
             return static::LOWER;
         }
 
+        if ($this->getParam('minValue') == $this->getParam('maxValue')) {
+            return self::EXACT;
+        }
+
         return static::BOTH;
     }
 }

tests/integration/rules/length_4.phpt

@@ -0,0 +1,16 @@
+--FILE--
+<?php
+
+require_once 'vendor/autoload.php';
+
+use Respect\Validation\Exceptions\LengthException;
+use Respect\Validation\Validator as v;
+
+try {
+    v::length(5, 5)->check('123456');
+} catch (LengthException $e) {
+    echo $e->getMainMessage();
+}
+?>
+--EXPECTF--
+"123456" must have a length of 5