Extending Sunit to Test Components

Although not included in the ANSI Smalltalk standard, SASE event frameworks have become a defacto standard feature of modern Smalltalk systems. SASE is a form of the Observer pattern [Gamma95] in which a subscriber requests of a specific publisher that it should notify that subscriber by sending it a specific message when an individual event occurs. This differs from the older dependency mechanism of Smalltalk-80, in which observers could not selectively subscribe to individual events, but instead received notifications of all events published, through a single callback. Both SASE and dependency mechanisms facilitate the construction of loosely coupled system in which the publishers of events need have no prior knowledge of the subscribers, and can have any number of the latter. The SASE mechanism has a number of advantages (and some disadvantages) over the dependency mechanism, which we will not go into here, and has largely superseded it, even in VisualWorks.