Testing cyclic software components of reactive systems on the basis of formal specifications

A bubble forming toy for the making of soap bubbles. The bubble toy comprises a housing in which a liquid soap solution is maintained, with a cover hinged to the top of the housing. A flexible air tube extends through the cover, and is fitted on the inside of the cover to a coil spring. The user closes the cover to wet the coil spring and then rotates the cover to an open position, blowing simultaneously through the flexible air tube to form bubbles from the solution retained on the coil spring.