Grammar test, math test, typing test, the people in the call center are very worried about attrition, if you just show them that you are desperate for the job(don't be too desperate, be cool) and have no plans of leaving, you want to grow in this field of work and are willing to do almost any thing (within certain limits of course), like working night shifts, working with rotating weekends,you don't really need a lot of leaves etc you're gonna get the job