1. OORPT Object-Oriented Reengineering Patterns and Techniques 10. Testing and Migration Prof. O. Nierstrasz

2. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.2 Roadmap  Tests: Your Life Insurance  Migration Strategies

3. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.3 Roadmap  Tests: Your Life Insurance —Write Tests to Enable Evolution —Grow Your Test Base Incrementally —Use a Testing Framework —Test the Interface, Not the Implementation —Write Tests to Understand —Record Business Rules as Tests —Other patterns  Migration Strategies

4. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.4 A Map of Reengineering Patterns Tests: Your Life Insurance Detailed Model Capture Initial Understanding First Contact Setting Direction Migration Strategies Detecting Duplicated Code Redistribute Responsibilities Transform Conditionals to Polymorphism

5. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.5 What and Why ? Definitions  Restructuring refers to transforming a system from one representation to another while remaining at the same abstraction level. — Chikofsky & Cross, ’90  Refactoring is the process of changing a software system in such a way that it does not alter the external behaviour of the code, yet improves its internal structure— Fowler, ’99 Motivation  Alter the source-code to —solve problems identified earlier —without introducing new defects —and while the system remains in operation

6. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.6 The Reengineering Life-Cycle Requirements Designs Code (0) requirement analysis (1) model capture (2) problem detection (3) problem resolution (4) program transformation (3) problem resolution (4) program transformation issues reliability time risk

7. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.7 Forces — Testing  Many legacy systems don’t have tests  Software changes introduce new bugs  You can’t test everything  Concurrency and user interfaces are hard to test  Testing is usually everyone’s lowest priority  Knowledge concentration poses high risk  Customers pay for features, not tests  Customers don’t want buggy systems  Good programmers don’t need tests  New tools and techniques are more fun than testing  Testing is akin to street-cleaning

8. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.8 Tests: Your Life Insurance Write Tests to Enable Evolution Grow Your Test Base Incrementally Managing tests Use a Testing Framework Test the Interface, Not the Implementation Record Business Rules as Tests Designing tests Write Tests to Understand Test Fuzzy features Test Old Bugs Retest Persistent Problems Regression Test after Every Change Migration Strategies

9. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.9 Write Tests to Enable Evolution Problem: How do you minimize the risks of change? Solution: Introduce automated, repeatable, stored tests Automated tests are the foundation of reengineering Long-term evolution System documentation Architectural evolution System Confidence Turnover Risk minimization Confidence in Change Automated Tests

10. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.10 Grow Your Test Base Incrementally  Problem: When can you stop writing tests?  Solution: When your tests cover all the code! —… however – you're paid to reengineer, not to write tests – testing ALL the code is impossible – design documentation is out-of date » semi-automated black-box testing is not an option Answer: Grow Your Test Base Incrementally first test critical components (business value; likely to change; …) keep a snapshot of old system (run new tests against old system) focus on business values test old bugs + new bugs that are reported Answer: Grow Your Test Base Incrementally first test critical components (business value; likely to change; …) keep a snapshot of old system (run new tests against old system) focus on business values test old bugs + new bugs that are reported

11. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.11 Use a Testing Framework  Problem: How do you encourage systematic testing?  Solution: Use a framework to structure your tests

12. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.12 Running tests

13. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.13 Test the Interface, Not the Implementation  Problem: How do you protect your investment in tests?  Solution: Apply black-box testing —Test interfaces, not implementations – Be sure to exercise the boundaries —Test scenarios, not paths – Use tools to check for coverage —Beware; – Enabling testing will influence your design!

14. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.14 Write Tests to Understand  Problem: How to decipher code without adequate tests or documentation?  Solution: Encode your hypotheses as test cases —Exercise the code —Formalize your reverse-engineering hypotheses —Develop tests as a by-product

15. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.15 Solution: Record Business Rules as Tests -canonical examples exist -can be turned into input/output tests Solution: Record Business Rules as Tests -canonical examples exist -can be turned into input/output tests Record Business Rules as Tests  Problem: How do you keep your system in sync with the business rules it implements?  A Solution: Good documentation + Good design —… however – business rules are too complex to design well – documentation & design degrades when the rules change – business rules become implicit in code and minds

16. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.16 Example: Payroll Business Rule  A person or couple gets an amount of money for every child he, she or they raise. Basically parents get CHF 150,- per month for every child younger than 12 years, and CHF 180,- for every child between 12 and 18 and for every child between 18 and 25 as long as the child is not working and is still in the educational system. A single parent gets the full 100% of this money as long as he or she is working more than 50%. Couples get a percentage of the money that is equal to the summed working percentages of both partners.

17. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.17 Example: Payroll Test Case "--- input-cases are extracted from a database" singlePerson80WithOneKidOf5 := extract.... couplePerson40occupationWithOneKidOf5 := extract.... couplePerson100occupationWithOneKidOf5 := extract.... couplePersonWithOneKidOf14 := extract.... "--- tests compare expected output against actual output" self assert: singlePerson80occupationWithOneKidOf5 moneyForKid = 150. self assert: couplePerson40occupationWithOneKidOf5 moneyForKid = 150*4. self assert: couplePerson100occupationWith2KidsOf5 moneyForKid = 150*2. self assert: couplePersonWithOneKidOf14 moneyForKid = 180.

18. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.18 Other patterns  Retest Persistent Problems —Always tests these, even if you are making no changes to this part of the system  Test Fuzzy Features —Identify and write tests for ambiguous or ill-defined parts of the system  Test Old Bugs —Examine old problems reports, especially since the last stable release —DeLano and Rising, 1998

19. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.19 Roadmap  Tests: Your Life Insurance  Migration Strategies —Involve the Users —Build Confidence —Migrate Systems Incrementally —Prototype the Target Solution —Always Have a Running Version —Regression Test After Every Change —Make a Bridge to the New Town —Present the Right Interface —Public vs. Published Interface —Deprecate Obsolete Interfaces —Conserve Familiarity —Use Profiler Before Optimizing

20. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.20 A Map of Reengineering Patterns Tests: Your Life Insurance Detailed Model Capture Initial Understanding First Contact Setting Direction Migration Strategies Detecting Duplicated Code Redistribute Responsibilities Transform Conditionals to Polymorphism

21. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.21 The Reengineering Life-Cycle Requirements Designs Code (0) requirement analysis (1) model capture (2) problem detection (3) problem resolution (4) program transformation (3) problem resolution (4) program transformation issues reliability time risk

22. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.22 Forces — Migration  Big-bang migration often fails  Users hate change  You need constant feedback to stay on track  Users just want to get their work done  The legacy data must be available during the transition

23. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.23 Migration Migrate Systems Incrementally Conserve Familiarity How Use Profiler before Optimizing Build Confidence Involve the Users How Why Prototype the Target Solution Always Have a Running Version Regression Test after Every Change Present the Right Interface Distinguish Public from Published Interfaces Deprecate Obsolete Interfaces Make a Bridge to the New Town How Tests, your Life-Insurance Tests, your Life-Insurance Where to

24. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.24 Involve the Users  Problem: How to get users to accept change?  Solution: Get them involved by giving them what they want —Start with the Most Valuable First —Prototypes can help raise enthusiasm, but may also raise expectations too high —Deploy early to increase commitment – Diverts energy from development – Pays back in quality feedback

25. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.25 Build Confidence  Problem: How do you overcome skepticism?  Solution: Deliver results in short, regular intervals —Requires time to sync with users —Requires effort to support the changes —Requires care not to alienate original developers —Requires regular, big demos to convince management

26. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.26 Migrate Systems Incrementally  Problem: When should you deploy the new system?  Solution: As soon as possible —Decompose the legacy system into parts —Tackle one part at a time (Most Valuable First) —Put suitable tests in place —Decide whether to wrap, reengineer, or replace —Deploy, support and obtain feedback —Iterate

27. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.27 Prototype the Target Solution  Problem: How do you evaluate the target solution?  Solution: Develop a prototype —Evaluate the technical risks – New system architecture – Migrating legacy data – Adequate performance … —Exploratory prototype? – Explore specific issues, then throw it away! —Evolutionary prototype? – Capture new architecture – Migrate, wrap, reengineer or reimplement parts

28. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.28 Always Have a Running Version  Problem: Maintaining confidence during development  Solution: Integrate changes on a daily basis —Use version and configuration management tools —Maintain exhaustive regression tests where needed —Plan short iterations — Continuous Integration – If necessary, re-architect the system to enable short build times

29. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.29 Regression Test After Every Change  Problem: Making sure changes don’t break the system  Solution: Run the regression tests at each “stable” point —You must relentlessly write tests! – Write new tests whenever new (untested) bugs are discovered – Take time to convince your team of the Joy of Testing —If testing takes too long, categorize tests – But run all the tests at least once a day —Consider writing tests up front —Remember to Retest Persistent Problems

30. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.30 Bridge 1:read()2:write() 1.1:read() 1.2:write()2.1:write() Legacy System New System Data Store Make a Bridge to the New Town  Problem: How to migrate data?  Solution: Convert the underlying files/databases/… —... however – Legacy and new system must work in tandem – Too much data; too many unknown dependencies – Data is manipulated by components

31. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.31 Present the Right Interface  Problem: How do you prevent the legacy design from polluting the new system?  Solution: Wrap old services as new abstractions —Identify the new abstractions you want —Wrap the legacy services to emulate the new interface – Avoid directly accessing old procedural interfaces – Avoid wrapping as pseudo-OO «utility» classes

32. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.32 Solution: Distinguish between “public” and “published” interface public = stable target interface published = available, but unstable (use at your own risk) language features (protected, friends, …) naming conventions Solution: Distinguish between “public” and “published” interface public = stable target interface published = available, but unstable (use at your own risk) language features (protected, friends, …) naming conventions Public vs. Published Interface  Problem: How to design interface for target solution?  Solution?: Think deeply —... however – Enable migration to target system ASAP – Avoid freezing the interface of target component – Costly ripple-effects of changes to public interface

33. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.33 Deprecate Obsolete Interfaces  Problem: How to modify an interface without invalidating all clients?  Solution: Flag the old interface as «deprecated» —Old and new interfaces can co-exist for a time – Deprecated usage can be lazily patched —Various techniques possible – Documentation (easy to ignore) – Move or rename old interfaces (painful) – Add warnings to deprecated code (should be non-intrusive)

34. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.34 Conserve Familiarity  Problem: How to avoid disrupting Users’ work?  Solution: Avoid radical changes —Avoid alienating users —Introduce a constant, small number of changes with each release

35. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.35 Use Profiler Before Optimizing  Problem: When should you rewrite inefficient code?  Solution: Only when you have benchmarks that prove it is worthwhile —“Do it, then do it right, then do it fast”

36. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.36 Conclusion  Avoid risk —small increments (“chicken little”) —develop suite of regression tests  … at acceptable cost —Migration costs as much as new development ! —But you avoid "hidden costs" – team morale in maintenance team – satisfying two customer bases

37. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz OORPT — CHAPTER X.37 License > http://creativecommons.org/licenses/by-sa/2.5/ Attribution-ShareAlike 2.5 You are free: to copy, distribute, display, and perform the work to make derivative works to make commercial use of the work Under the following conditions: Attribution. You must attribute the work in the manner specified by the author or licensor. Share Alike. If you alter, transform, or build upon this work, you may distribute the resulting work only under a license identical to this one. For any reuse or distribution, you must make clear to others the license terms of this work. Any of these conditions can be waived if you get permission from the copyright holder. Your fair use and other rights are in no way affected by the above. Attribution-ShareAlike 2.5 You are free: to copy, distribute, display, and perform the work to make derivative works to make commercial use of the work Under the following conditions: Attribution. You must attribute the work in the manner specified by the author or licensor. Share Alike. If you alter, transform, or build upon this work, you may distribute the resulting work only under a license identical to this one. For any reuse or distribution, you must make clear to others the license terms of this work. Any of these conditions can be waived if you get permission from the copyright holder. Your fair use and other rights are in no way affected by the above.