This document discusses generating characterization tests for legacy code. It describes characterization tests as tests that characterize the actual behavior of code to act as change detectors and protect legacy code from unintended changes. It provides an example of a characterization test for a calculation method, and discusses how to find "pinch points" in code to focus testing and how to structure tests to replay inputs and outputs from recorded method executions. The document also introduces a framework for writing characterization tests by recording method inputs, outputs, and dependencies.

1. Generating Characterization Tests for Legacy CodeJonas 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 coveragehttp://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. @RecordingpublicintexampleMethod(intparameter, intparameter2) {returnparameter+parameter2;}@DependencypublicStringinvokedMethodOnDependency(Stringargument) {returnargument.toUpperCase();}

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