Design by Contract (DbC) is a methodology to construct quality software. DbC associates the contract pecification (pre and postconditions of methods of class and class invariant) with the design of a class. In this paper, we combine data flow testing and Design by Contract to develop a testing technique called “Data flow testing using Contract”. In this technique a class flow graph is generated from the contract specification of the class and then conventional data flow testing is applied to find the test cases. The advantage of using contract specification is that: it is executable and hence a method in a test case is only executed if its precondition and class invariant are satisfied. If they are not satisfied then it leads to an infeasible sequence. Also, if after executing a method its postcondition is not satisfied then it leads to implementation error in the method. We also compare the testing of a DbC class with a conventional class and find that the number of du pairs is reduced in a DbC class because some of the conditions in conventional class become the part of the precondition in a DbC class.