Preserving externally Observable Behavior

A finite set of external actions that the program may perform defines the observable behavior of a program. Refactoring is a disciplined process of applying structural transformations in the code such that the program is improved in terms of quality and its external behavior is preserved. Refactoring includes evaluation of its preconditions, execution of its mechanics and corrective actions required to retain the behavior of the program. These transformations affect various locations throughout a program which includes its clients and unit tests. Due to the complex dependencies involved with in the program, preservation of program behavior often becomes nontrivial. The guidelines on refactoring by Fowler [1] lack precision and leave opportunities for developers to err. In this paper, we analyze and present an exhaustive categorization of refactoring guidelines based on their impact on production and test code together. In order to formalize the existing refactoring guidelines, we rewrite them using the primitive behavior preserving refactorings by Opdyke [19]. In addition these extended refactoring guidelines also adapt the clients and unit tests to keep them syntactically and semantically aligned with the refactored code. KeywordsRefactoring Guideline; Unit testing; Production Code; Test Code, Adaptation