Index: modules/field/field.test
===================================================================
RCS file: /cvs/drupal/drupal/modules/field/field.test,v
retrieving revision 1.11
diff -u -r1.11 field.test
--- modules/field/field.test	20 Apr 2009 02:46:22 -0000	1.11
+++ modules/field/field.test	28 Apr 2009 03:53:20 -0000
@@ -989,7 +989,7 @@
     }
 
     // Check that invalid field names are rejected.
-    $field_definition['field_name'] += '_#';
+    $field_definition['field_name'] .= '_#';
     try {
       field_create_field($field_definition);
       $this->fail(t('Cannot create a field with an invalid name.'));