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

OORPTObject-Oriented Reengineering Patterns and Techniques

10. Testing and Migration

Prof. O. Nierstrasz

© Stéphane Ducasse, Serge Demeyer, Oscar Nierstrasz

OORPT — CHAPTER

X.2

Roadmap

> Tests: Your Life Insurance> Migration Strategies


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


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


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


OORPT — CHAPTER

X.6

The Reengineering Life-Cycle

Requirements

Designs

Code

(0) requirementanalysis

(1) modelcapture

(2) problemdetection (3) problem

resolution

(4) program transformation

(3) problem resolution(4) program transformationissues• reliability• time• risk


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


OORPT — CHAPTER

X.8


Write Tests to Enable Evolution

Grow Your TestBase Incrementally

Managing testsUse a Testing

Framework

Test the Interface,Not the Implementation

Record BusinessRules as Tests

Designingtests

Write Teststo Understand

• Test Fuzzy features• Test Old Bugs• Retest Persistent Problems

Regression Testafter Every Change

Migration StrategiesMigration Strategies


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 evolutionLong-term evolution

System documentationSystem documentation Architectural evolutionArchitectural evolution

System ConfidenceSystem Confidence Turnover Risk minimizationTurnover Risk minimization Confidence in ChangeConfidence in Change

Automated TestsAutomated Tests


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


OORPT — CHAPTER

X.11

Use a Testing Framework

> Problem: How do you encourage systematic testing?> Solution: Use a framework to structure your tests


OORPT — CHAPTER

X.12

Running tests


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!


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


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


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.


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.


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


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


OORPT — CHAPTER

X.20

A Map of Reengineering Patterns


Detailed Model Capture

Initial Understanding

First Contact

Setting Direction

Migration Strategies

Detecting Duplicated Code

Redistribute Responsibilities

Transform Conditionals to Polymorphism


OORPT — CHAPTER

X.21

The Reengineering Life-Cycle

Requirements

Designs

Code

(0) requirementanalysis

(1) modelcapture

(2) problemdetection (3) problem

resolution

(4) program transformation

(3) problem resolution(4) program transformationissues• reliability• time• risk


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


OORPT — CHAPTER

X.23

Migration

Migrate SystemsIncrementally

ConserveFamiliarity

HowUse Profiler

before Optimizing

Build ConfidenceInvolve the UsersHow Why

Why

Prototype theTarget Solution

Always Have aRunning Version

Regression Testafter Every Change

Present theRight Interface

Distinguish Publicfrom Published Interfaces

DeprecateObsolete Interfaces

Make a Bridgeto the New Town

How

Tests, yourLife-Insurance

Tests, yourLife-Insurance

Where to


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


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


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


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


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


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


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


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


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


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)


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


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”


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


OORPT — CHAPTER

X.37

License

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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 2.5You 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.

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

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