An automated way to detect differences in the values of program variables/expressions and the order of execution between one run and another. A collection mode saves the values of expressions/variables at collection points in the program. On a subsequent execution during the detection mode, these saved values of the same expressions/variables are recalled and compared with the current values. Advantageously, the user selects the collection points within the program at which variable information can be gathered and compared; and these collection points may include: breakpoints set by a debugging program or by the user; collection points set by the user, and entry and/or exit points and/or points within program structures, such as procedure calls, control blocks, etc. Setup of the collection mode includes the capability to modify the expressions/variables, the tolerance or the acceptable alternatives, and the position and number of collection points.