the main coverage tecniques used in the software industry are white box testing and black box testing. in the black box testing we don't need to bother about code just we have to know about the specifications.
EX: in calculator we don't need to worry about code , just testing whether it gives 4+3=7 or not like that.

where as in white box we have to observe the code line by line whether  it is executing or not.  there are different tecniques in white box like branch testing , statement testing. in statement testing we have write test cases to execute each and every statement only , where as in the branch testing we have to cheak for each side of branch and each statement.  For better understanding read ISEB meterial from BCS. ORG