OORPT CHAPTER OORPT Object-Oriented Reengineering Patterns and

OORPT — CHAPTER OORPT Object-Oriented Reengineering Patterns and Techniques 10. Testing and Migration Prof. O. Nierstrasz © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz

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

OORPT — CHAPTER 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 © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz 3

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

OORPT — CHAPTER 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 © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz 5

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

OORPT — CHAPTER 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 © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz 7

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

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

OORPT — CHAPTER 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 © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz 10

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

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

OORPT — CHAPTER 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! © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz 13

OORPT — CHAPTER 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 © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz 14

OORPT — CHAPTER 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 Solution: Record Business Rules as Tests - canonical examples exist - can be turned into input/output tests © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz 15

OORPT — CHAPTER 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. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz 16

OORPT — CHAPTER Example: Payroll Test Case "--- input-cases are extracted from a database" single. Person 80 With. One. Kid. Of 5 : = extract. . couple. Person 40 occupation. With. One. Kid. Of 5 : = extract. . couple. Person 100 occupation. With. One. Kid. Of 5 : = extract. . couple. Person. With. One. Kid. Of 14 : = extract. . "--- tests compare expected output against actual output" self assert: single. Person 80 occupation. With. One. Kid. Of 5 money. For. Kid = 150. self assert: couple. Person 40 occupation. With. One. Kid. Of 5 money. For. Kid = 150*4. self assert: couple. Person 100 occupation. With 2 Kids. Of 5 money. For. Kid = 150*2. self assert: couple. Person. With. One. Kid. Of 14 money. For. Kid = 180. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz 17

OORPT — CHAPTER 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 — De. Lano and Rising, 1998 © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz 18

OORPT — CHAPTER 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 © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz 19

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

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

OORPT — CHAPTER 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 © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz 22

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

OORPT — CHAPTER 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 © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz 24

OORPT — CHAPTER 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 © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz 25

OORPT — CHAPTER 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 © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz 26

OORPT — CHAPTER 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 © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz 27

OORPT — CHAPTER 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 © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz 28

OORPT — CHAPTER 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 © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz 29

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

OORPT — CHAPTER 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 © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz 31

OORPT — CHAPTER 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 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 © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz 32

OORPT — CHAPTER 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) © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz 33

OORPT — CHAPTER 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 © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz 34

OORPT — CHAPTER 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” © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz 35

OORPT — CHAPTER 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 © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz 36

OORPT — CHAPTER License > http: //creativecommons. org/licenses/by-sa/2. 5/ Attribution-Share. Alike 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. © Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz 37