Sometimes the actual contents of a data field are different from what they are supposed to be. For example, a numeric field in one or more records may contain alphabetic data because of a program error or a clerical mistake. Also, a field may contain corrupted data because of an error in the file-flattening process. Whatever the cause, prior to performing any substantive tests on a new file, it is important to validate its contents. Invalid data will distort the test results and may cause a system failure.