Unit Testing: Control Your Dependencies!

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Unit Testing:  Control Your Dependencies! Jon Reid — @qcoding  Facebook

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Write a failing test Make the test pass Refactor

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UI? Networking?

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UI! Networking!

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http://www.ﬂickr.com/photos/jsmoorman/2298671281 3 Types of  Unit Tests: ! Return Value Test ! State Test ! Interaction Test

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Return Value Test Arrange: Set up object Act: Call method that returns a value Assert: Compare against expected value Test SUT call method value System Under Test

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State Test Arrange: Set up object Act: Call method Assert: Query object in some way Test SUT call method result query

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Interaction Test Test SUT Something Else! ? ?

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Interaction Test Table GetDishes Waiter Cook ProcessOrder

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Interaction Test Table GetDishes Waiter Cook ProcessOrder Fake Cook

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Dependency Injection Table GetDishes Waiter Cook ProcessOrder Fake Cook

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Dependency Injection • Extract and Override • Method Injection • Property Injection • Constructor Injection http://www.ﬂickr.com/photos/8499561@N02/2755481069

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No content

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Seams http://www.ﬂickr.com/photos/gileslane/2262575575

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Extract and Override

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Extract and Override

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Method Injection

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Method Injection

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Property Injection

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Property Injection

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Property Injection

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Constructor Injection

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Dependency Injection • Extract and Override • Method Injection • Property Injection • Constructor Injection • Ambient Context http://www.ﬂickr.com/photos/8499561@N02/2755481069

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Dependency Injection M A N N I N G Mark Seemann FOREWORD BY GLENN BLOCK in .NET

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Interaction Test SUT Real Thing SUT Fake Thing Production Testing ?

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Types of Fakes M A N N I N G the art of with examples in C# FOREWORDS BY Michael Feathers Robert C. Martin SECOND EDITION ROY OSHEROVE

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Stub Test SUT Stub communicate assert (Fake)

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Mock Test SUT Mock communicate assert (Fake)

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“That’s great, Jon. …But how do I use this for networking?”

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Networking Call Inject dependency

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Networking Call Record number of calls

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Networking Call Fake return value

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Networking Call Capture arguments

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Let’s Make a Fake

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Let’s Make a Fake: 1. Stub the method

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Let’s Make a Fake: 2. Record number of calls

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Let’s Make a Fake: 3. Fake return value

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Let’s Make a Fake: 4. Capture arguments

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Let’s Write a Test (1): Does it call GET exactly once? 1. Arrange ! 2. Act  3. Assert

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Let’s Write a Test (2): Simulate a JSON Response!

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Refactor Test Code: Spot Duplication

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Refactor Test Code: Move Variables into Test Fixture

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Refactor Test Code: Use Test Fixture

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Refactor Test Code: Extract Helper Method Refactor test code to express the scenario

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Let’s Make a Fake • Stub the method • Record number of calls • Fake return value • Capture arguments Fake Cook

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Dependency Injection • Extract and Override • Method Injection • Property Injection • Constructor Injection http://www.ﬂickr.com/photos/8499561@N02/2755481069

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http://www.ﬂickr.com/photos/jsmoorman/2298671281 3 Types of  Unit Tests: ! Return Value Test ! State Test ! Interaction Test

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QualityCoding.org @qcoding • Working Effectively with Legacy Code by Michael Feathers • Dependency Injection in .NET by Mark Seemann • The Art of Unit Testing by Roy Osherove • Test-Driven iOS Development by Graham Lee Resources