Show instance name in instanceOf error message

src/Valitron/Validator.php

@@ -736,6 +736,10 @@ class Validator
             }
             if ($param instanceof \DateTime) {
                 $param = $param->format('Y-m-d');
+            } else {
+                if(is_object($param)) {
+                    $param = get_class($param);
+                }
             }
             // Use custom label instead of field name if set
             if(is_string($params[0])) {

tests/Valitron/ValidateTest.php

@@ -829,6 +829,19 @@ class ValidateTest extends BaseTestCase
       $this->assertTrue($v->validate());
     }
 
+    public function testInstanceOfErrorMessageShowsInstanceName()
+    {
+      $v = new Validator(array('attributeName' => new Validator(array())));
+      $v->rule('instanceOf', 'attributeName', new stdClass());
+      $v->validate();
+      $expected_error = array(
+        "attributeName" => array(
+          "AttributeName must be an instance of 'stdClass'"
+        )
+      );
+      $this->assertEquals($expected_error, $v->errors());
+    }
+
     public function testInstanceOfInvalidWithString()
     {
       $v = new Validator(array('attributeName' => new stdClass()));