Dr. Dobb's Journal - March 2008 - (Page 34)

Core Technology CHANGE CODE WITHOUT FEAR continued from page 32 team just received a new requirement to implement a discount policy—25 percent of the discount will be applied to the total price if the weighted average price per individual item is greater than $20. To implement this requirement, the getSubTotal() method of the com.ibatis.jpetstore.domain.Cart class needs to be changed. Listing Four (available online) implements the new idea. You can change this code without fear of unknowingly introducing problems. The regression test suite alerts you if your code modifications introduced any undesired results. When you rerun the regression suite against the modified code, you get one assertion failure and one case where the test fails due to an ArithmeticException; see Figure 3. Taking a closer look at the ArithmeticException failure, you notice that the new code is introducing a defect because it is not properly handling a case when the number of items in the cart is 0. The problematic line is marked with the comment //Division by zero. The code should be modified to check whether the total number of items in the cart is not equal to 0 before it proceeds to perform the division. For example: if (totalItems !=0) { BigDecimal actualAvePrice = subTotal.divide(new BigDecimal (totalItems)); if (actualAvePrice.compareTo (targetAvePrice) > 0) { //if avg price is $20 or more, let's apply 25% discount BigDecimal sb = new BigDecimal(0.75); subTotal = subTotal.multiply (sb).setScale(2); } } Figure 3: Running the regression suite against modified code. When you rerun the regression test suite, the ArithmeticException failure is no longer reported. In this case, the regression suite prevented you from introducing a defect into the code. Next look at the reported assertion failure. It indicates that a test case was expecting the order total to be $112, but it was actually $84. This failure occurs in the functional BuyDogandCatTest test case (Listing Three), which was added to the regression suite. Given the new discount policy in place, this is actually the correct behavior—not a defect. This means that the test needs to be updated to remain in sync with the source code change. In this case, the expected amount in the assertion needs to be changed from $112 to $84. If you rerun the regression suite after this change is made, no failures are reported. DDJ 34 Dr. Dobb’s Journal l www.ddj.com l March 2008 http://www.codejock.com http://www.codejock.com http://www.ddj.com

Table of Contents Feed for the Digital Edition of Dr. Dobb's Journal - March 2008

Dr. Dobb's Journal - March 2008 Contents Hmmmm Alia Vox Developer Diaries Developer’s Notebook Social Networks and Software Development Conversations Detecting Bugs in Safety-Critical Code Change Code Without Fear Continuous Integration and Performance Testing Wt: A Web Toolkit Automating Release Notifications The Agile Edge Effective Concurrency Swaine’s Flames

Dr. Dobb's Journal - March 2008

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.