Answer the following:-(software engineering question)

i)How are the test cases designed for the alpha beta and acceptance testing?Are te test cases for the three types of tests necessarily identical?

ii)Usability of software product is tested during which type of testing:unit,integration,system testing?How usability is tested?

iii)Suppose a developed software has successfully passed all the three levels of testing i.e.,unit ,integration and system testing.Can you claim that software is defect free?Justify