title: How to randomize the case of letters in a string
body: <p>I want to write some automated tests for web app authentication. The login password is case-sensitive and always contains at least one alphabetic character.</p>
  
  <p>I want to write a test where I randomly change the case of one or more alphabetic characters.</p>
  
  <p>Let's say the password string is <code>"123te123st!"</code>.</p>
  
  <p>Now I want to change this string to one which contains at least one uppercase letter. I'm trying to make sure that the login is still case-insensitive and any variation in case will fail to match the password.</p>
  
  <p>Does anybody know a elegant way to do it? I searched already (including Apache Commons) but couldn't find a helper method.</p>