Generating characterization tests for legacy code

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

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

How the development team felt...

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

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

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

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

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

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

Test run completed. Results 1/1 passed.

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

…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/

~85% code coveragehttp://www.flickr.com/photos/shuttercat7/713186211/

// 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.}

[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}

~300 fast characterization tests

http://follesoe.github.com/BlackBoxRecorder

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

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

<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>

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

http://github.com/oc/jackbox

@RecordingpublicintexampleMethod(intparameter, intparameter2) {returnparameter+parameter2;}@DependencypublicStringinvokedMethodOnDependency(Stringargument) {returnargument.toUpperCase();}

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

Generating characterization tests for legacy code

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