Web applications are often exposed to unpredictable work-loads, which makes computing resource management di-cult. The resource may be overused when the workload is high and underused when the workload is low. A solution to deal with unpredictable workloads is to migrate Web applications to cloud computing infrastructures, where the resource is varied according to demand, i. e., elasticity. With elasticity, all the resource variations happen during the Web application runtime. To deal with this, the Web application , and its service layers must behave in an elastic manner , which comprises adaptation tasks. These tasks may introduce functional and non-functional errors into the Web application. To nd these errors, we must test the Web application when the adaptation tasks are performed, during the resource variations. Some tests may require a specic sequence of resource variations, which are dicult to be achieved without controllability. Therefore, in this paper, we propose an approach that controls the required resource variations. We validated our approach by conducting several experiments on Amazon EC2 cloud infrastructures. In these experiments, we successfully lead the Web application through the required resource variations.