Using Combinations to Improve Your Software Test Case Generation

摘要

Combinations are an indispensable tool in planning and executing configuration testing, especially in a sub-area called interaction analysis. Suppose.for example, you need to test your product on a machine with multiple browsers and multiple media players installed. You want to test your system in conjunction with three browsers installed from a pool of eight browsers, and with two media players installed from a pool of six players. How many configuration combinations are there? How can you programmati-cally list these configurations? The techniques presented in this column make it easy for you to calculate that there are Choose(8,3) * Choose(6, 2) = 840 possible test configurations. It also allows you to easily list all of them programmatically. Combinations are useful when examining and testing paths of execution. I'll illustrate with a classic problem that is a surrogate for analyzing paths of execution (problems like this example are often used in interviewing test engineer candidates at Microsoft). Suppose you are developing a game. Players enter the southwest corner of a room with a tiled floor. Players must move to the northeast corner of the room by moving one tile to the east or one tile to the north (in other words players are always moving in the direction of the exit and do not backtrack). If the room is small―only 10 tiles by 6 tiles―how many different paths can the player take?