1. 14 July 2011 © Agile Institute 2011 1 Café TDD? Sure, but What About My Legacy Code? Rob Myers for Test Driven Developers Bay Area 14 Jul 2011

2. What is “Legacy Code”? 14 July 2011 © Agile Institute 2011 2

3. 14 July 2011 © Agile Institute 2011 3 “Code we’re afraid to change.” -- James Shore “Code without tests.” -- Michael Feathers

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5. Adding Tests Is Difficult 14 July 2011 © Agile Institute 2011 5 Circumstantial coupling: "I can’t test this without instantiating half the system!" Peculiar encapsulation: “I wish I could just test that private method!” Duplication:"I'll have to test this on all the subclasses!" Poor cohesion: "This MasterControlClass does everything, so the test will be enormous and complex!"

6. A Conundrum 14 July 2011 © Agile Institute 2011 6 We add tests to refactor safely. We have to refactor to add safe tests.

7. 14 July 2011 © Agile Institute 2011 7 What could possibly go wrong?!

8. Choose Your Battles Test the code you need to change now (unless it is very difficult) Test the code that changes most often (even if it is difficult) Test the code that haunts your nightmares! 14 July 2011 © Agile Institute 2011 8

9. Write “Pinning” Tests We don’t add or change behavior. We’re not bug-hunting. We aim for coverage. We must see GREEN. 14 July 2011 © Agile Institute 2011 9

10. Technique: “The Three Questions” What behavior needs test coverage? What’s preventing us from writing a test? What can we do about that? 14 July 2011 © Agile Institute 2011 10

11. Technique:Separate Behavior from Initialization It’s easier to test behavior when not coupled to initialization code. Use ‘Extract Method’ to preserve existing interfaces. 14 July 2011 © Agile Institute 2011 11

12. Before 14 July 2011 © Agile Institute 2011 12 public void OpenOrderReport( OutputGadget output, string accountNumber) { Account account = LunExData.QueryAccount(accountNumber); Order[] openOrders = LunExData.QueryOrders( "open", accountNumber, DateTime.Now); foreach (Order order in openOrders) { // ... output.Write("Order #" + order.Number); // ... } }

13. After ‘Extract Method’ 14 July 2011 © Agile Institute 2011 13 public void OpenOrderReport( OutputGadget output, string accountNumber) { Account account = LunExData.QueryAccount(accountNumber); Order[] openOrders = LunExData.QueryOrders( "open", accountNumber, DateTime.Now); FormatOpenOrderReport(output, account, openOrders); } private void FormatOpenOrderReport( OutputGadget output, Account account, Order[] openOrders) { foreach (Order order in openOrders) { // ... output.Write("Order #" + order.Number); // ...

14. Technique:Expose A Private Variable or Method Make a method public (at least accessible to tests) Wrap a variable in getter/setter methods. It may smell really bad. It will eventually be a useful addition to the interface, or will move to another object. 14 July 2011 © Agile Institute 2011 14

15. Before 14 July 2011 © Agile Institute 2011 15 private void FormatOpenOrderReport( OutputGadget output, Account account, Order[] openOrders) { foreach (Order order in openOrders) { // ... output.Write("Order #" + order.Number); // ... } }

16. After 14 July 2011 © Agile Institute 2011 16 public void FormatOpenOrderReport( OutputGadget output, Account account, Order[] openOrders) { foreach (Order order in openOrders) { // ... output.Write("Order #" + order.Number); // ... } }

17. Technique:Wrap, Then Mock Add a simple delegating Proxy to… Code we cannot change. Final (Java) or sealed (.NET) classes. Classes with no accessible constructors. Anything with a broad (mostly-unused) interface. Feathers’s “Adapt Parameter” is an example of this. 14 July 2011 © Agile Institute 2011 17

18. Delegating Proxy 14 July 2011 © Agile Institute 2011 18 ObjectUnderTest + MethodToTest() BrainlessProxy XYZZY + intFoo() + string Bar(int) + intFoo() + string Bar(int) + double Baz()

19. A New Production Class 14 July 2011 © Agile Institute 2011 19 public class BrainlessProxy { private XYZZY realOne; public BrainlessProxy(XYZZY theRealXYZZY) { this.realOne = theRealXYZZY; } public virtual intFoo() { return realOne.Foo(); } public virtual string Bar(int parameter) { return realOne.Bar(parameter); } }

20. Tough Problem (Simple Example) 14 July 2011 © Agile Institute 2011 20 public class TrafficLight { public void SwitchLights() { Color newColor; if (currentColor.IsRed()) newColor = new Green(); else if (currentColor.IsGreen()) newColor = new Yellow(); else newColor = new Red(); currentColor.Flash(); Pause(3); currentColor.StopFlashing(); newColor.LightUp(); currentColor.Off(); currentColor = newColor; }

21. Technique:Factory-Method Injection Extract a Factory Method for the dependency. Let the test create a “Testable” subclass of the Object Under Test. TestableFoo overrides the Factory Method and injects the mock. 14 July 2011 © Agile Institute 2011 21

22. Before ‘Extract Method’ 14 July 2011 © Agile Institute 2011 22 public void SwitchLights() { Color newColor; if (currentColor.IsRed()) newColor = new Green(); else if (currentColor.IsGreen()) newColor = new Yellow(); else newColor = new Red(); currentColor.Flash(); Pause(3); currentColor.StopFlashing(); newColor.LightUp(); currentColor.Off(); currentColor = newColor; }

23. After ‘Extract Method’ part I 14 July 2011 © Agile Institute 2011 23 public void SwitchLights() { Color newColor; newColor = NextColor(currentColor); currentColor.Flash(); Pause(3); currentColor.StopFlashing(); newColor.LightUp(); currentColor.Off(); currentColor = newColor; }

24. After ‘Extract Method’ Part II 14 July 2011 © Agile Institute 2011 24 private Color NextColor(Color currentColor) { Color newColor; if (currentColor.IsRed()) newColor = new Green(); else if (currentColor.IsGreen()) newColor = new Yellow(); else newColor = new Red(); return newColor; }

25. A Small Change 14 July 2011 © Agile Institute 2011 25 protected virtual Color NextColor(Color currentColor) { Color newColor; if (currentColor.IsRed()) newColor = new Green(); else if (currentColor.IsGreen()) newColor = new Yellow(); else newColor = new Red(); return newColor; }

26. The Test, Part 1 14 July 2011 © Agile Institute 2011 26 public static MockColornewColor; [TestMethod] public void TrafficLightSwitchTurnsNextColorOn() { newColor = new MockColor(); TrafficLighttrafficLight = new TestableTrafficLight(); trafficLight.SwitchLights(); Assert.IsTrue(newColor.WasTurnedOn()); }

27. The Test, Part 2Override Just the Factory Method 14 July 2011 © Agile Institute 2011 27 public class TestableTrafficLight : TrafficLight { protected override Color NextColor(Color currentColor) { return newColor; } } public class MockColor : Color { bool wasLit = false; public override void LightUp() { wasLit = true; } public bool WasTurnedOn() { return wasLit; } }

28. When to Use a Factory Method “I don’t know, but…” If creation of the dependency is buried deep within conditional code. If the Factory Method is (or can be) used in multiple places. If Dependency Injection seems worse (e.g. at a published API). 14 July 2011 © Agile Institute 2011 28

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31. 14 July 2011 © Agile Institute 2011 31 Rob.Myers@agileInstitute.com http://PowersOfTwo.agileInstitute.com/