Use case scenarios are created during the analysis phase to specify software system requirements and can also be used for creating system level test cases. Using use cases to get system tests has several benefits including test design at early stages of software development life cycle that reduces over all development cost of the system. Current approaches for system testing using use cases involve functional details and does not include guards as passing criteria i.e. use of class diagram that seem to be difficult at very initial level which lead the need of specification based testing without involving functional details. In this paper, we proposed a technique for system testing directly derived from the specification without involving functional details. We utilize initial and post conditions applied as guards at each level of the use cases that enables us generation of formalized test cases and makes it possible to generate test cases for each flow of the system. We used use case scenarios to generate system level test cases, whereas system sequence diagram is being used to bridge the gap between the test objective and test cases, derived from the specification of the system. Since, a state chart derived from the combination of sequence diagrams can model the entire behavior of the system.Generated test cases can be employed and executed to state chart in order to capture behavior of the system with the state change.All these steps enable us to systematically refine the specification to achieve the goals of system testing at early development stages.