Below And Beneath TDD

Test-Last Development and other real world test patterns

Noel Rappin@noelrap

Pathfinder Developmentpathf.com

railsprescriptions.com

http://www.railsrx.com

Rx

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Why does testing work?

Why does testing fail?

Rx

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testing to “work”?

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Improve effectiveness of team and

quality of code

NOT

A perfect guarantee ofcode correctness

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for me, tdd is about confidence &

accountability & responsibility & design &

reusability & portability & flexibility & testing & trustworthiness &

teamwork & initiative & flow & that's all i can

think of at the moment.

-- Kent Beck

Rx

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Accurate view of code

Small, incremental steps

Scaffold for change

Focus for development

Rx

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testing to “fail”?

Rx

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code quality

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“It feels like there's a hidden door that everyone who tests has found and

walked through... There are a bunch of us...that would love to join

the party, but don't know where to find

the door.”

Rx

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If you are stuck in a window or banging your head against the wall,

this will helpyou get to the door

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PASSTest-Driven

Development

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AKA: Behavior-DrivenDevelopment

or

Test-FirstProgramming

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TDD Code has:

small pieceshigh cohesionloose coupling

minimal side-effects

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☺Accurate view of code

☺Small, incremental steps

☺Scaffold for change

☺Focus for development

Rx

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PASS

Rx

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CODE

PASSLose the refactoring

Rx

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PASSDevelopment, that

happensto have tests

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PASS

Symptoms:

Increased duplicaton in code.

Long methods

Rx

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CODE

PASS

Benefits:

May seem faster at first

Rx

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FAIL

CODE

PASSOver time...

Rx

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CODE

PASS

☺Accurate view of code

Small, incremental steps

Scaffold for change

☺Focus for development

Rx

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CODE

PASSFix by:

Cleaning up your mess

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Rx

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TEST

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TEST

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assert_equal(nil, actual)

actual = 4.314

assert_equal(4.314, actual)

Rx

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CODE

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TEST

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Data-Driven Testing

or

Using your programas a calculator

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TEST

FAIL

Benefits:

Failed Test Guaranteed

Value may be hard to calculate

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CODE

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TEST

FAIL

Pitfalls:

Can mask ignoranceof domain

Can lead to worseproblems

Rx

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CODE

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TEST

FAIL

Accurate view of code

☺Small, incremental steps

☺Scaffold for change

☺Focus for development

Rx

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FAIL

CODE

REFACTOR

PASS

TEST

FAIL

assert_equal(nil, actual)

actual = 4.314

assert_equal(4.314, actual)

Rx

CODE REFACTOR

PASS

TEST

actual = 4.314

assert_equal(4.314, actual)

Rx

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CODE REFACTOR

PASS

Test-Next Development

aka

Code-Driven Development

Rx

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Symptoms:

No more failing tests

Tweaking tests to match code

Coverage drop

Rx

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PASS

Benefits:

Useful when exploring

Useful when testingviews

Rx

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Pitfalls:

Easily slides into worsepatterns

Hard to avoidcoverage gaps

Rx

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Accurate view of code

☺Small, incremental steps

Scaffold for change

Focus for development

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PASSTautology Based

Development

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Definition:

Tests that can’tfail

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PASS

Symptoms:

Bugs that should have been covered

Mock objectmisuse

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☹Accurate view of code

☺Small, incremental steps

Scaffold for change

☹Focus for development

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Mitigation:

Try to separatecode assertions from application

data

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Rx

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PASS

CODE

CODE

CODE

CODE

CODE

CODE

Rx

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PASS

CODE

CODE

CODE

CODE

CODE

CODE

Test-Last Development

Rx

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CODE

CODE

CODE

CODE

CODE

CODE

Symptoms:

Significant coverage drop

Uncovered bugs

Harder to write tests

Rx

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CODE

CODE

CODE

CODE

CODE

CODE

This is one way in which we talk past each other

Unit tests ≠ TDD

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CODE

CODE

CODE

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Pitfall:

Tests get moreexpensive

Lower quality tests

Programmer boredom

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CODE

CODE

CODE

CODE

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Needed when:

Hitting corner case

Dealing with legacy

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CODE

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☹Accurate view of code

☹Small, incremental steps

Scaffold for change

☹Focus for development

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CODE

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Escape by:

Start the TDD process

Don’t look back

Catch up to legacyparts as you touch

them

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CODE

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CODE

CODE

CODE

Rx

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Run

CODE

CODE

CODE

CODE

CODE

CODE

Rx

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Run

CODE

CODE

CODE

CODE

CODE

CODE

Coverage Driven Development

Rx

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Run

CODE

CODE

CODE

CODE

CODE

CODE

Symptom:

Tests without assertions

Rx

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Run

CODE

CODE

CODE

CODE

CODE

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Why?

Minimal approach to legacy

Hard to reach code

Rx

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Run

CODE

CODE

CODE

CODE

CODE

CODE

☹Accurate view of code

☹Small, incremental steps

☹Scaffold for change

☹Focus for development

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Rx

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TESTTEST

TESTTEST

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TESTTEST

TESTTEST

Lots of Test First Development

Rx

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TESTTEST

TESTTESTSymptom:

Lots of test failures atonce during initial developmment

Rx

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TESTTEST

TESTTESTBenefit:

Allows planning for future code

Rx

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TESTTEST

TESTTEST Cost:

Loss of focus

Somewhat harder towrite code against

Rx

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TESTTEST

TESTTEST

Middle Ground:

RSpec pending

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TESTTEST

TESTTEST☺Accurate view of code

Small, incremental steps

☺Scaffold for change

Focus for development

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Rx

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SETUP

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SETUP

Setup Driven Development

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SETUPSymptom:

Large, brittle setup methods

Slow tests

High-level tests

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SETUPCosts:

This is why people hate testing

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SETUPAccurate view of code

☹Small, incremental steps

☺Scaffold for change

Focus for development

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SETUPEscape by:

Mock Objects

Real unit tests

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Another problem:

End to end failures

Lack of focus

Expectation failures

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Cucumber

A potential solution

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Cucumber

Acceptance Test-DrivenDevelopment

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Cucumber

Symptom:

You are writing acceptance tests

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Cucumber

Costs:

Additional layer of test code, indirection

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Cucumber

Benefits:

Increased focus, improved feedback

Rx

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Cucumber

☺Accurate view of code

☺Small, incremental steps

☺Scaffold for change

☺Focus for development

Rx

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FAIL

CODE

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PASS

Rx

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And So:

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Constant feedbackand

baby steps

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Focus on what comes next

Failure Driven Development

Rx

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Good code has

small pieceshigh cohesionloose coupling

minimal side-effects

Rx

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FAIL

CODE

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PASS

Invisible cost of bugs

or

Done vs. “Done Done”

Rx

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PASSGo write

some tests!

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Rails Test Prescriptions

http://www.railsrx.com

Pathfinder Development

http://www.pathf.comhttp://www.pathf.com/blogs

@noelrap @railsrx

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