Lightning talk from JavaZone 2010 on generating characterization tests for legacy code.

1. Generating Characterization Tests for Legacy Code Jonas Follesø (@follesoe) JavaZone 2010, 09. September

2. Huge methods (~3000+ lines)

3. Dave & Karin http://www.flickr.com/photos/dnk_uk/3525103502/ ~50 slow integration tests

4. How the development team felt...

5. What they needed

6. What I read

7. Legacy code is code without tests. Code without tests is bad code. -Michael C. Feathers Fraser Speirs http://www.flickr.com/photos/fraserspeirs/3395595360/

8. A characterization test is test that characterizes the actual behavior of a piece of code. It acts as a change detector, protecting legacy code form unintended changes

9. publicdoubleCalc(doubleinv, doublert, inty) { doubleret=0; for (inti=1; i<=y; i++) { ret=inv*Math.Pow(1.0+rt/100.0, i); } returnret; }

10. [TestMethod] publicvoidCalc_characterization() { varcalc=newCalcUtil(); doubleresult=calc.Calc(10000, 10, 10); Assert.AreEqual(42.0, result); }

11. Assert.AreEqual failed. Expected:<42>. Actual:<25937.424601>.

12. [TestMethod] publicvoidCalc_characterization() { varcalc=newCalcUtil(); doubleresult=calc.Calc(10000, 10, 10); Assert.AreEqual(42, result); Assert.AreEqual(25937.424601, result); }

13. Test run completed. Results 1/1 passed.

14. publicdoubleCalculateCompoundInterest(doubleinvestment, doubleinterest, intyears) { doubleprojectedValue=0.0; for (intyear=1; year<=years; year++) { projectedValue=investment* Math.Pow(1.0+interest/100.0, year); } returnprojectedValue; }

15. …A pinch point is a natural encapsulation boundary. When you find a pinch point, you’ve found a narrow funnel for all the effects of a large piece of code… -Michael C. Feathers Fraser Speirs http://www.flickr.com/photos/fraserspeirs/3395599536/

16. ~85% code coverage http://www.flickr.com/photos/shuttercat7/713186211/

17. // This method is the "pinch point" we want to test... publicobjectCalculateSomething(objectsomeParameter) { // 1) Record input parameters... // 2) Do the work... // 3) Write parameters and return value to XML file. }

18. [TestMethod] publicvoidCalculateSomething_test1() { Run("Recordings/CalculateSomething1.xml"); } [TestMethod] publicvoidCalculateSomething_test2() { Run("Recordings/CalculateSomething2.xml"); } publicvoidRun(stringfilename) { // Load input parameters from XML file // Load return value from XML file // Call method under test // Use reflection to compare actual vs. recorded }

19. ~300 fast characterization tests

20. How can we reuse this?

21. http://follesoe.github.com/BlackBoxRecorder

22. [Recording]

23. [Dependency]

24. [Recording] publicList<EmployeeEntity>GetMakingMoreThan(doublesalary) { vardal=newEmployeeDAL(); varemployees=dal.GetAllEmployees(); returnemployees.Where(e=>e.Salary>salary).ToList(); }

25. [Dependency] publicclassEmployeeDAL { publicList<EmployeeEntity>GetAllEmployees() { // Calls to database... } }

26. <Recording> <Name>GetEmployeesMakingMoreThan_salary</Name> <Method>GetEmployeesMakingMoreThan</Method> <Type><![CDATA[BlackBox.Demo.App.SimpleAnemic.EmployeeBL]]></Type> <InputParameters> <Parameter> <Name>salary</Name> <Type><![CDATA[System.Double]]></Type> <Value><![CDATA[5000]]></Value> </Parameter> </InputParameters> <Return> <Type><![CDATA[List<BlackBox.Demo.App.SimpleAnemic.EmployeeEntity>]]></Type> <Value><![CDATA[XML representation of employees retruned from method]]></Value> </Return> <Dependencies> <Dependency> <Type><![CDATA[BlackBox.Demo.App.SimpleAnemic.EmployeeDAL]]></Type> <Method> <Name>GetAllEmployees</Name> <ReturnValues> <ReturnValue> <Value><![CDATA[XML representation of all employees returned from db]]><Value> </ReturnValue> </ReturnValues> </Method> </Dependency> </Dependencies> </Recording>

27. [TestMethod] publicvoid GetEmployeesMakingMoreThan_salary() { Run(@"GetEmployeesMakingMoreThan_salary.xml"); }

28. http://github.com/oc/jackbox

29. @Recording publicintexampleMethod(intparameter, intparameter2) { returnparameter+parameter2; } @Dependency publicStringinvokedMethodOnDependency(Stringargument) { returnargument.toUpperCase(); }

30. Jonas Follesø Senior Consultant +47 977 06660 Jonas.folleso@bekk.no / jonas@follesoe.no