Test engineers can see the results of Test code coverage to help them create Test cases & input or configuration sets to increase code coverage of vital functions. Four common forms of code coverage used by pollster’s statement (or line) coverage, & path (or edge) coverage. Line reports on the coverage footprint of the implementation of evidence in terms of lines of code that is executed to complete the Test. Edge coverage reports which branches or points of code is executed the decision to complete the Test. They document a coverage metric, measured in percentage. Code coverage is a white box testing activity. The target application is built with special options or libraries & / or run in a special environment that every function that is exercised (executed) in the program (s) are apportioned back to the function points in the source code. This process allows developers & quality assurance personnel to find parts of a process that never or never accessed under normal conditions (error handling & the like) & helps to reassure the Test engineers that the most important conditions (function points) have been tested. In general, tools & code coverage libraries exact a performance & / or memory, or the cost of other resources that is unacceptable to normal operations of the application. Therefore only used in the laboratory. As expected there's kinds of application are not likely to take these tests for coverage, despite a degree of coverage of the mapping can be approximated through analysis than direct evidence. There’s also some types of defects are affected by these tools. In particular, the operations of positive race conditions or similar real-time sensitive can be masked when jogging on code coverage environments, & conversely, a number of these defects may become less hard to find as a result of overloading Additional Test code.