Help! My Legacy Application is Unmaintainable!

HELP! My Legacy Application is Unmaintainable!

Reducing the cost of change in legacy code bases

John Ferguson Smart

Consultant Trainer Mentor Author Speaker Coder

Legacy applications are difficult to maintain

Legacy applications generate revenue

What is a legacy application?

Old code base?


Outdated technology


“Legacy code is code without tests”!!

- Michael Feathers

But what is wrong with legacy code?

Nothing…if you don’t need to change it much

…it is hard to add new features

Legacy code is bad when…

…changes risk introducing regressions


…poor coding style and/or lack of documentation makes the code hard to understand


…there are no automated tests


…it prevents you from delivering as quickly as you would like


Why not just rewrite it all?

Over &me, new features get harder and harder to add

Cumulated effort to add new

features

Time

Total cost to maintain the

legacy application

Cost of not rewri&ng

What do we really want?

We need to be able to make the changes we need to make faster and more reliably

So how can we get changes out faster?

Build a safety net

Document the specifications

Build a safety net

Characterisation Test!!

A means to describe (characterise) the actual behaviour of an existing piece of software, and therefore protect existing behaviour of legacy code against unintended changes. !

Term coined by Michael Feathers

Broad, high level automated acceptance tests

Application

To write good automated tests

do not write tests

Write a user’s manual instead…

…but automate it

Automate user journeys

Organise your requirements

Browse the product catalogView product detailsSearch for products

Organise your requirements Browse the product catalogView product detailsSearch for products

Illustrate behaviour using examples

Document your business rules

Good automated acceptance tests have layersMake them maintainable

Use layers!

Keep them tidy

Business Rules

Business Flow

Page/Component interac&ons

Page/Component details

Good automated acceptance tests have layersMake them maintainable

Start with high-level requirements

Drill down into more detailed requirements

Illustrate a requirement with tests

Documenting the specifications

A question of style

Spock

context["When cumulating Frequent Flyer points"] = () => { it["should earn points for each flight"] = () => { member.earnStatusPoints(100); member.earnStatusPoints(50); member.getStatusPoints().should_be(150); }; ! it["should get upgrade when enough points are earned"] = () => { member.earnStatusPoints(00); ! member.getStatus().should_be(Status.Silver); }; }; } } NSpec

A question of style

JUnit

Adding new features

TDD/BDD outposts in the wilderness

Discussion Time!

ReferencesBDD In Action - Manning

http://thucydides.info

http://www.wakaleo.com

Help! My Legacy Application is Unmaintainable!

Technology

Transcript of Help! My Legacy Application is Unmaintainable!