Existing program is restructured based on a set of tasks that the existing program executes. A set of tasks is used, in conjunction with related test cases, to verify the correct functioning of the restructured program, and also to restructure the program. The restructuring process involves information about: (i) the tasks for which the original computer program is used, (ii) the inputs (including their valid ranges) to be provided to the program to accomplish the tasks, and (iii) the outputs generated by the program, known but unfixed bugs, etc. Legacy computer programs or applications for which reliable documentation is either not available or inadequate is desirably restructured for improved understanding and maintenance.