What are the steps need to take care before closing the design verification project

how do you know bugs are not available in the design (How will you sure the whole environment working correctly or not) before closing the project verification??, please help me in this.

In reply to Subbi Reddy:

You have to meet the requirements of your verification plan, i.e. you have enogh tests to verify the verification requirements, you meet your coverage goals (line and functional) and your assertions are correct.