test driven development: why i hate it; but secretly love it

Test Driven Development

Why I hate it, but really love it.

Start with FAIL

Make it Green!

Make it Pretty (refactor)

(Not Like this chap)

Eh?

• Why???• How???• When???

WHY TDD?

Stability

Flexibility

Documentation

MORE SPEEEEDzzz

Design

HOW TDD?

(Disclaimer: Code incoming!)

• Failing Test:

def test_add_1_plus_1 assert_equal 2, add(1,1)end

Output:tdd.rb:6:in `test_add_1_plus_1': undefined method `add' for main:Object (NoMethodError)from tdd.rb:9

Writing an adding, er.. Thing…

WHATS THE NEXT STEP?

• Make it pass:

def add(i,j) return 2endOutput:Loaded suite TddExampleStarted.Finished in 0.000455 seconds. 1 tests, 1 assertions, 0 failures, 0 errors

Waait!! Why isn’t it just:

def add(i,j) return i+jend

WHATS THE NEXT STEP?

Write another failing test:

def test_add_1_plus_2 assert_equal 3, add(1,2)End

Loaded suite TddExampleStartedFFinished in 0.042739 seconds. 1) Failure:test_add_1_plus_1(TddExample) [tdd.rb:42]:<3> expected but was<2>. 1 tests, 1 assertions, 1 failures, 0 errors

Make it pass:

def add(i,j) return i+jEnd

Loaded suite TddExampleStarted..Finished in 0.000462 seconds.

2 tests, 2 assertions, 0 failures, 0 errors

All about the baby steps

Problems?

add(1,2,3)

Fail.

add(1,”two”)

Fail.

How do we cope?

• Any number of arguments?• First add a test..

def test_adding_three_arguments assert_equal 4, add(1,2,1)End

Make it pass!!

Add another test!!

def test_adding_four_arguments assert_equal 8, add(1,2,1,4)end

Refactor

For the general solution:

def add(*args) return args.inject(0){|sum,n| sum + n}End

Loaded suite TddExampleStarted....Finished in 0.000941 seconds. 4 tests, 4 assertions, 0 failures, 0 errors

Dependency Injection(This has nothing to do with children)

Example:

class PersonDAO def initialize(user, password) @data_source = Database.connect(user,

password) endend

VS

class PersonDAO def initialize(data_source) @data_source = data_source endend

Why is this better?

And you’re telling me this… why?

Start off with a test

def setup @person = FamilGuyDao.newend

def test_return_full_name_is_reginald_von_griffen assert_equal "Reginald Von-Griffin",

@person.full_nameend

#But how do we make it vary? Pass in the name? Pull it from somewhere #Lets assume there is some Griffin Family Tree in the sky

def test_return_full_name_is_stewie_griffin assert_equal "Stewie Griffin", @person.full_name end

For now we’ll pass in the name

Next Test….

Make it pass…

WHATS THE NEXT STEP?

• The General Case

Integration faked by Mock object!

MAKE IT PASS!!

DONE!