This presentation will give you a fuller understanding of unit testing in Swift, its benefits, key characteristics, mocks and stubs, dependency injection, DI patters and common mistakes one may make throughout the process. This presentation by Andrii Gavrysh, GlobalLogic expert, was delivered at GlobalLogic Lviv iOS TechTalk on November 16, 2016. Learn more: https://www.globallogic.com/ua/gl_news/globallogic-lviv-ios-techtalk-summary

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Unit Testing in Swift
Andrii Gavrysh

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1. Testing and its levels
2. Unit testing
3. Benefits
4. Key characteristics of unit test
5. Mocks and Stubs
6. Dependency injection
7. DI patterns
8. Common mistakes
Agenda

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Testing and it’s levels

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Testing and it’s levels
Integration testing answers the question “How do components/modules/systems work
together?”
Unit testing helps ensure that every single unit of our program always works correctly.
Unit testing
Integration testing

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Unit testing is a testing technique using
which individual modules are tested to
determine if there are any issues by the
developer himself. It is concerned with
functional correctness of the standalone
modules.
Unit testing
• It is a technique
• Performs testing of individual modules
• Using to determine issues in application
units
• Written by developers for developers
Definition Something simpler…

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• Captures the current state of code
• Reduces bugs when changing the existing functionality
• Improves design and allows better refactoring of code
• Helps to understand code for which tests were written
• Shows the quality of build
Benefits

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• Independence
• Fast execution
• Test only logic of one unit
Key characteristics of unit test

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OK
Enough for boring theory!!!
Let’s test something!

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Guinea pig
Any ideas how to test this?

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Prepare your mind and code for
testing

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1. Create dummy service classes
2. Replace original classes execution with dummy ones
Simple testing strategy

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1. Create dummy service classes

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There are two types of classes that are used in unit testing for preventing real
code to be executed - mocks and stubs. Both of them have the same interface as
replacing object.
Stub – replaces real class logic with predefined results.
Mock – mimics the behavior of real object and is pre-programmed with some
expectations.
Mocks and Stubs

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Example
Stub Mock

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• Setup - Prepare object that is being tested
and its stubs collaborators.
• Exercise - Test the functionality.
• Verify state - Use asserts to check
object's state.
• Teardown - Clean up resources.
Flow during test execution
• Setup - Prepare object that is being
tested.
• Setup expectations - Prepare
expectations in mock that is being used
by primary object.
• Exercise - Test the functionality.
• Verify expectations - Verify that correct
methods have been invoked in mock.
• Verify state - Use asserts to check
object's state.
• Teardown - Clean up resources.
Stub Mock

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2. Replace original classes
execution with dummy ones

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Dependency injection is an answer to the question “How?”
Two simple rules:
• Each class-service(dependency) should be passed to your class from outside
• Class must depend on abstraction, not on specific classes.
Dependency injection

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Three base patterns for Dependency Injection
Constructor Setter
Interface

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Results

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Do you remember the initial
implementation?

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Do you remember the initial implementation?

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If make it more realistic then…

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Service locator is a central registry which on request returns necessary information to
perform a certain task.
Service Locator
Definition

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Example

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OK
What about DBProvider?

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• Type resolver represents a registry not for class objects, but for class types.
Type resolver

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Example

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Usage

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In tests

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Common mistakes

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• Asynchronous calls
• Calls to persistence
• Not clearing singletons state
• Running production ApplicationDelegate
• Focusing on code coverage
• Do not run tests
• Ignore test results
• Commented tests
Bad things list

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Questions?

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Thank you