diff --git a/Test/Unit/Visitor/Asserter.php b/Test/Unit/Visitor/Asserter.php
new file mode 100644
index 0000000..3feed20
--- /dev/null
+++ b/Test/Unit/Visitor/Asserter.php
@@ -0,0 +1,85 @@
+<?php
+
+/**
+ * Hoa
+ *
+ *
+ * @license
+ *
+ * New BSD License
+ *
+ * Copyright © 2007-2015, Ivan Enderlin. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *     * Redistributions of source code must retain the above copyright
+ *       notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above copyright
+ *       notice, this list of conditions and the following disclaimer in the
+ *       documentation and/or other materials provided with the distribution.
+ *     * Neither the name of the Hoa nor the names of its contributors may be
+ *       used to endorse or promote products derived from this software without
+ *       specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS AND CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+namespace Hoa\Ruler\Test\Unit\Model;
+
+use Hoa\Test;
+use Hoa\Ruler as LUT;
+
+/**
+ * Class \Hoa\Ruler\Test\Unit\Model\Asserter.
+ *
+ * Test suite of the asserter object of the visitor.
+ *
+ * @author     Alexis von Glasow <alexis.von-glasow@hoa-project.net>
+ * @copyright  Copyright © 2007-2015 Alexis von Glasow.
+ * @license    New BSD License
+ */
+
+class Asserter extends Test\Unit\Suite {
+
+    public function case_keep_errors ( ) {
+        $this
+            ->given(
+                $ruler     = new LUT(),
+                $fExecuted = false,
+                $asserter  = $ruler->getDefaultAsserter(),
+                $asserter->setOperator(
+                    'f',
+                    function ( $a = false ) use ( &$fExecuted ) {
+
+                        $fExecuted = true;
+
+                        return $a;
+                    }
+                ),
+                $rule = 'f(false)'
+            )
+            ->when($result = $ruler->assert($rule, new LUT\Context()))
+            ->then
+                ->boolean($result)
+                    ->isFalse()
+                ->boolean($fExecuted)
+                    ->isTrue()
+                ->boolean($asserter->hasError())
+                    ->isTrue()
+                ->array($asserter->getErrors())
+                    ->isNotEmpty()
+                    ->hasKey('f')
+            ;
+    }
+}
+
diff --git a/Visitor/Asserter.php b/Visitor/Asserter.php
index 66991a1..3db8da8 100644
--- a/Visitor/Asserter.php
+++ b/Visitor/Asserter.php
@@ -67,6 +67,13 @@ class Asserter implements Visitor\Visit {
      */
     protected $_operators = [];
 
+    /**
+     * List of errors.
+     *
+     * @var \Hoa\Ruler\Visitor\Asserter array
+     */
+    protected $errors = [];
+
 
 
     /**
@@ -159,6 +166,10 @@ protected function visitOperator ( Ruler\Model\Operator $element, &$handle = nul
             $value       = $argument->accept($this, $handle, $eldnah);
             $arguments[] = $value;
 
+            // Add operators name and their values in errors lists
+            if (false === $value)
+                $this->errors[$element->getName()] = $element->getArguments();
+
             if($element::LAZY_BREAK === $element->shouldBreakLazyEvaluation($value))
                 break;
         }
@@ -487,4 +498,37 @@ public function getOperators ( ) {
 
         return $this->_operators;
     }
+
+    /**
+     * Get all errors.
+     *
+     * @access  public
+     * @return  array
+     */
+    public function getErrors ( ) {
+
+        return $this->errors;
+    }
+
+    /**
+     * The evaluation of operators has it raised errors.
+     *
+     * @access  public
+     * @return  boolean
+     */
+    public function hasError ( ) {
+
+        return !empty($this->errors);
+    }
+
+    /**
+     * Reset all errors raised
+     *
+     * @access  public
+     * @return  void
+     */
+    public function resetErrors ( ) {
+
+        $this->errors = [];
+    }
 }