1. A computer-implemented method 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 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.