Writing Testable Code Alvaro Videla - Cloud Foundry About Me - - PowerPoint PPT Presentation

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Writing Testable Code Alvaro Videla - Cloud Foundry About Me - - PowerPoint PPT Presentation

Mar 21, 2023 241 likes •820 views

Writing Testable Code Alvaro Videla - Cloud Foundry About Me Cloud Foundry Developer Advocate Blog: http://videlalvaro.github.com/ Twitter: @old_sound About Me Co-author RabbitMQ in Action http://bit.ly/rabbitmq Im not a:

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Writing Testable Code

Alvaro Videla - Cloud Foundry

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About Me

  • Cloud Foundry Developer Advocate
  • Blog: http://videlalvaro.github.com/
  • Twitter: @old_sound
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About Me

Co-author RabbitMQ in Action http://bit.ly/rabbitmq

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I’m not a:

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I’m not a:

  • Application Testing Guru
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I’m not a:

  • Application Testing Guru
  • TDD Advocate
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Why is it so hard to write tests?

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Unit Testing

The goal of unit testing is to isolate each part of the program and show that the individual parts are correct

http://en.wikipedia.org/wiki/Unit_testing

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Unit Testing

[…] unit testing by definition only tests the functionality of the units themselves.

http://en.wikipedia.org/wiki/Unit_testing

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Unit Testing

[…] Therefore, it will not catch integration errors or broader system-level errors (such as functions performed across multiple units, or non-functional test areas such as performance)

http://en.wikipedia.org/wiki/Unit_testing

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Dogma vs. Reality

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A world of Trade Offs

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What should we test?

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How much should we test?

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“I get paid for code that works, not for tests, so my philosophy is to test as little as possible to reach a given level of confidence” – Kent Beck

http://stackoverflow.com/questions/153234/how-deep-are-your-unit-tests/153565#153565
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The Hidden Secret Of TDD

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The Secret of TDD

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The Secret of TDD

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Some books by Kent Beck

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To write good tests first we need to learn how to program

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We developers are like those users we like to complain so much about

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Design evolves and matures with time

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Good Code sits in the small details

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TIPS

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Separate pure code from impure or stateful

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Pure Functions

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Pure Functions

  • Referential Transparency
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Pure Functions

  • Referential Transparency
  • Don’t modify external state
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Pure Functions

  • Referential Transparency
  • Don’t modify external state
  • Don’t produce side effects
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What’s wrong with this code?

if($player->getScore() > 0) { $player->setSwizzle(7); } else { $player->setSwizzle( $player->getSwizzle() + 1 ); }

https://dl.dropboxusercontent.com/u/7810909/docs/what-does-fp-mean/what-does-fp-mean/chunk-html/ar01s05.html
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What’s wrong with this code?

$newScore = $player->getScore() > 0 ? 7 : $player->getSwizzle() + 1; $player->setSwizzle($newScore);

https://dl.dropboxusercontent.com/u/7810909/docs/what-does-fp-mean/what-does-fp-mean/chunk-html/ar01s05.html
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Score calculation can be moved into its own function

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Score calculation can be tested now

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First write Pure Code

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Add impure code step by step when needed

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Write Composable Code

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Function Composition

http://en.wikipedia.org/wiki/Function_(mathematics)
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Function Composition

http://en.wikipedia.org/wiki/Function_(mathematics)
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This looks familiar

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“Many UNIX programs do quite trivial tasks in isolation, but, combined with other programs, become general and useful tools.”

http://math.albany.edu/math/pers/hammond/unixphil.html
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Number of open connections per IP

netstat -ntu | awk '{print $5}' | \ cut -d: -f1 | sort | uniq -c | sort -n

http://www.commandlinefu.com/commands/view/1767/number-of-open-connections-per-ip.
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Why don’t we just code in this style?

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This seems familiar again…

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Welcome to Functional Programming

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“Writing unit tests is reinventing functional programming in non-functional languages”

http://noss.github.io/2009/02/25/writing-unit-tests-is-reinventing-functional-programming-in-non-functional-languages.html
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What can we learn from Functional Programming?

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The proper use of Types

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What does ‘null’ mean?

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What does ‘true|false’ mean?

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Functions with just one responsibility

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Radical separation of pure code from impure code

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Let’s see an example

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Food for Thought

http://thinking-forth.sourceforge.net

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“Inside every well- written large program is a well-written small program”

http://www.linfo.org/q_programming.html
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Questions?

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Thanks!

http://twitter.com/old_sound http://github.com/videlalvaro http://www.slideshare.net/old_sound