Upgrade to Pro — share decks privately, control downloads, hide ads and more …

Characterization Testing : regaining control o...

Characterization Testing : regaining control of your Legacy Code [EN]

Many companies are struggling with a significant legacy code base. They know it but are afraid of attacking the issue because they’ve been burned before with never-ending refactoring. Unit tests can help, but how do you handle the legacy code? This session will look at how "characterization" tests can tackle the vicious cycle of technical debt!

More Decks by Félix-Antoine Bourbonnais

Other Decks in Programming

Transcript

  1. & FÉLIX-ANTOINE BOURBONNAIS B.ING., M.SC, PSM Version: Mai 2017 (DEV)

    Characterization Testing : regaining control of your Legacy Code PASCAL ROY ING., CSM, PSM, PMP
  2. Think how Legacy code affects your work in everyday life…

    Imagine a tool that helps you explore, understand and refactor it without fear. … a nice dream, isn’t?
  3. 4 Qui sommes-nous ? Pascal Roy Ing., PSM, CSM, PMP

    Félix-Antoine Bourbonnais B.ing., PSM, M.Sc.
  4. Speakers Trainers Coaches & Mentors Tech. Team & Business Mgmt.

    TDD Emergent architecture Automated tests DDD … Scrum Agile QA Project management Agility BDD > We are Strategic advice > What we do
  5. Code that is difficult to modify and evolve. Regardless how

    old it is or why it got this way. What is Legacy Code ?
  6. • Code written by others • Code nobody wants to

    touch anymore • Code no longer supported by the people who wrote it • Code that could be rewritten using better coding practices, tools or languages • ... Other popular definitions …
  7. Tired of the continuous stress of delivery, of endless debugging

    sessions, of the fear of breaking something?
  8. Overcome fear! To… Understand and document what the code does

    Protect against unintended changes when refactoring +
  9. 1. Find and isolate a piece of code that you

    need to analyze or modify 2. Write a test that uses that code, use an assertion you know will fail 3. Execute the test and let it tell you the actual behavior 4. Change the test assertion and the naming to match the actual behavior 5. Repeat… 5 steps for writing a characterization test
  10. public class SalesUtil { double BQ = 1000.0; double BCR

    = 0.20; double OQM1 = 1.5; double OQM2 = OQM1 * 2; public double calculate(double tSales) { if (tSales <= BQ) { return tSales * BCR; } else if (tSales <= BQ * 2) { return (BQ) * BCR + (tSales - BQ) * BCR * OQM1; } else { return (BQ) * BCR + (tSales - BQ) * BCR * OQM1 + (tSales - BQ * 2) * BCR * OQM2; } } } http://s3.amazonaws.com/giles/demons_010609/wtfm.jpg An example of Legacy Code? WTF? WTF? WTF?
  11. public class SalesUtil { double BQ = 1000.0; double BCR

    = 0.20; double OQM1 = 1.5; double OQM2 = OQM1 * 2; public double calculate(double tSales){ if (tSales <= BQ) { return tSales * BCR; } else if (tSales <= BQ * 2) { return (BQ) * BCR + (tSales - BQ) * BCR * OQM1; } else { return (BQ) * BCR + (tSales - BQ) * BCR * OQM1 + (tSales - BQ * 2) * BCR * OQM2; } } } @Test public void test… { assert(...) } Step 1: identify a piece of code to characterize 1 ? 2 ? ? 1 2
  12. public class SalesUtil { double BQ = 1000.0; double BCR

    = 0.20; double OQM1 = 1.5; double OQM2 = OQM1 * 2; double calculate(double tSales) { if (tSales <= BQ) { return tSales * BCR; } else if (tSales <= BQ * 2) { return (BQ) * BCR + (tSales - BQ) * BCR * OQM1; } else { return (BQ) * BCR + (tSales - BQ) * BCR * OQM1+ (tSales - BQ*2)*BCR * OQM2; } } } @Test public void testCalculate() { assertEquals( 0.0, SalesUtil.calculate(1000.0) ); } Step 2: write a failing assertion 1 ? 2 ? ? 1 2
  13. public class SalesUtil { double BQ = 1000.0; double BCR

    = 0.20; double OQM1 = 1.5; double OQM2 = OQM1 * 2; double calculate(double tSales) { if (tSales <= BQ) { return tSales * BCR; } else if (tSales <= BQ * 2) { return (BQ) * BCR + (tSales - BQ) * BCR * OQM1; } else { return (BQ) * BCR + (tSales - BQ) * BCR * OQM1 + (tSales - BQ * 2) * BCR * OQM2; } } } @Test public void testCalculate() { assertEquals( 0.0, SalesUtil.calculate(1000.0) ); } Step 3: execute the test + find out the actual behavior is > junit.framework.AssertionFailedError: expected:<0.0> but was:<200.0> 1 ? 2 ? ?
  14. public class SalesUtil { double BQ = 1000.0; double BCR

    = 0.20; double OQM1 = 1.5; double OQM2 = OQM1 * 2; double calculate(double tSales) { if (tSales <= BQ) { return tSales * BCR; } else if (tSales <= BQ * 2) { return (BQ) * BCR + (tSales - BQ) * BCR * OQM1; } else { return (BQ) * BCR + (tSales - BQ) * BCR * OQM1+ (tSales – BQ*2)*BCR * OQM2; } } } @Test public void lessThanBaseQuota_useBaseCommissionRate() { assertEquals( 200.0, SalesUtil.calculate(1000.0) ); } Step 4: Replace the assertion by the actual behavior 1 2 1 200 2 ? ?
  15. public class SalesUtil { double BQ = 1000.0; double BCR

    = 0.20; double OQM1 = 1.5; double OQM2 = OQM1 * 2; double calculate(double tSales) { if (tSales <= BQ) { return tSales * BCR; } else if (tSales <= BQ * 2) { return (BQ) * BCR + (tSales - BQ) * BCR * OQM1; } else { return (BQ) * BCR + (tSales - BQ) * BCR*OQM1+ (tSales – BQ*2) * BCR*OQM2; } } } … @Test public void testCalculate () { assertEquals( 0.0, SalesUtil.calculate(2000.0) ); } Step 5: Repeat 1 2 1 200 2 ? ?
  16. Watch out for : « While we’re at it, we

    might as well… » ! Work only on what you need to modify now.
  17. How long does it take to understand a piece of

    Legacy code before you can change it (reasonably safely)?
  18. • Specifies required behavior • Known behavior and new code

    • Permanent • Specifies actual behavior • Legacy code, Lost or forgotten behavior • Temporary Unit test Characterization test How is a CT different?
  19. A big expense Big Bang Very high risk No new

    business value Regular payments (debt) Step by Step Lower risk Still produce value Rewrite Renovate / Rejuvenate Rewrite or refactoring ?!?
  20. A strategy > stabilize the patient and focus on what

    is most critical As in the emergency room…
  21. This talk was about understanding and securing your Legacy Code….

    Now, you can learn how to mercilessly renovate your Legacy Code: • Sprout Methods/Classes • Instance Delegator • Extract to Method • … Next… Refactoring techniques
  22. Although our first joy of programming may have been intense,

    the misery of dealing with legacy code is often sufficient to extinguish that flame. Michael Feathers, Working Effectively with Legacy Code Legacy code can kill the flame!
  23. Site elapsetech.com Twitter @fbourbonnais Email [email protected] [email protected] LinkedIn linkedin.com/in/fbourbonnais ca.linkedin.com/in/roypa

    conferences.elapsetech.com All our conferences (french) conferences.elapsetech.com /legacy-tests-caracterisation Slides and references (french) Félix-Antoine Bourbonnais Pascal Roy