Replaced string check with simpler logic. Passes unit tests.

Author: kschroeder

app/code/Magento/Customer/Model/Customer/Attribute/Backend/Password.php

@@ -53,16 +53,7 @@ public function beforeSave($object)
                 );
             }
 
-            if ($this->string->substr(
-                $password,
-                0,
-                1
-            ) == ' ' || $this->string->substr(
-                $password,
-                $length - 1,
-                1
-            ) == ' '
-            ) {
+            if (trim($password) != $password) {
                 throw new LocalizedException(__('The password can not begin or end with a space.'));
             }