14. A computer program product for detecting an influence caused by changing a source code of an application from which a document object model (DOM) tree and cascading style sheets (CSSs) are extracted, the computer program product comprising a computer readable storage medium having program instructions embodied therewith, the program instructions executable by a processor to cause the processor to perform a method comprising: saving one or more input operations of a user of the application, a DOM tree, and a CSS for each of one or more times that an instruction is received to check a screen state; emulating, after the source code is changed, the one or more input operations in an operation order, for each of the one or more times; acquiring a DOM tree and CSS for each of the one or more times; comparing the saved DOM tree and CSS with the acquired DOM tree and CSS for each of the one or more times; and outputting a result of the comparison.
14. A computer program product for detecting an influence caused by changing a source code of an application from which a document object model (DOM) tree and cascading style sheets (CSSs) are extracted, the computer program product comprising a computer readable storage medium having program instructions embodied therewith, the program instructions executable by a processor to cause the processor to perform a method comprising: saving one or more input operations of a user of the application, a DOM tree, and a CSS for each of one or more times that an instruction is received to check a screen state; emulating, after the source code is changed, the one or more input operations in an operation order, for each of the one or more times; acquiring a DOM tree and CSS for each of the one or more times; comparing the saved DOM tree and CSS with the acquired DOM tree and CSS for each of the one or more times; and outputting a result of the comparison. 20. The computer program product of claim 14 , wherein: the saving further comprises capturing a first screenshot of the application for each of the one or more times; the emulating further comprises capturing a second screenshot of the application at each of the one or more times; and the outputting further comprises displaying each of the first screenshot captured in the saving and the second screenshot acquired in the emulating, as the result of the comparison.