Test Driven Development Part 2Designing Testable (Clean) Code

by @mcbeelenHaarlem Software Developer Meetup

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Meetup Sponsor:

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“Clean Code that works” by Ron Jeffries / Kent Beck:

1. meets the requirements passes the tests

2. reveals intention the code is easy to understand

3. contains no duplication DRY: Once and only Once

4. Build with fewest number of elements Remove everything else:

YAGNI!

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Loose Coupling – High Cohesion

Methods in classesClasses in filesClasses in packagesPackages in a module

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com.klm......modelcom.klm.....databasecom.klm.....servicecom.klm.....rest

Package by Feature com.klm.....airportcom.klm.....citycom.klm.....museumscom.klm.....restaurants

Package by Layer

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Change is local

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Mind sized componentsMaximum of number lines of code in a method?

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hasGoodNames() isSolid()

adheresToLawOfDemeter()

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Use words from the Ubiquitous Language.

A common, rigorous language to be usedbetween developers and users, without any ambiguity.

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Just say the words!

01-10-2015 Confidential Page 18http://arlobelshee.com/good-naming-is-a-process-not-a-single-step/

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Each component has just 1 responsibility.All parts of such a component should be related to that single responsibility.

Any logic is implemented in just one place.

Just one programming language per file

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Law of Demeter

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Law of Demeter

In a method of an object you are ONLY allowed to talk to:1. The object itself.

to call other methods of this object

2. The parameters of the method.to get access to information (or to invoke a callback)

3. Object created within that method.in order to delegate responsibility

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Law of Demeter

payAmountDue(customer, amount) { wallet = customer.getWallet(); return wallet.getMoney(amount);}

payAmountDue(customer, amount) { return customer.askForMoney(20);}

Customer.askForMoney(amount) { return myWallet.getMoney(amount)}

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http://www.planetgeek.ch/2014/11/18/clean-code-cheat-sheet-v-2-4/

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1. You are here to LEARN. (and have fun)

2. Try to do your best.

3. Work in pairs.Find a partner in a similar programming language and operating system

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Game of Life Kata

See you next time: March 2ndTest Driven Development

Driving Development by Tests Haarlem Software Developer Meetup