Unit Testing in Android

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Unit Testing in Android Anuj Middha Niharika Arora ADG Delhi Senior Software Engineer,1mg

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Agenda ● Introduction to App Architecture and Unit Tests ● Tools and Frameworks ● Writing Testable Code ● Demo

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Good/Clean Code Base? What is that?Why should we have good/clean code base?

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Scalable | Stable | Testable | Modular

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Application Architecture Why do I care?

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MV* Patterns MV (C | P | VM) 1. Data source of the application 2. Network layer, database operations Model

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MV* Patterns MV (C | P | VM) Responsible for displaying data View

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MV* Patterns MV (C | P | VM) Controller manipulates, edit, uses data model and show it to users via View. In Android, Activity/Fragments can act as both View and Controller Controller

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MV* Patterns MV (C | P | VM) Presenter is a simple java class that do not contain any UI components, it just manipulates data from model and display in on View. Presenter

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MV* Patterns MV (C | P | VM) They provide data and functionality to be used by views. They are what define the structure and behavior of the actual application you are building ** Many View can be mapped to one View-Model ViewModel

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MVC vs MVP vs MVVM Which one to follow?

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Activity/Fragment/View should be Business logic free

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Unit Test “ A software testing method by which individual units of code, are tested to determine whether they are ﬁt for use. The smallest testable part of an application (Classes and Methods).

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Anatomy of a unit test ▪ Arrange all necessary preconditions and inputs. ▪ Act on the object or method under test. ▪ Assert that the expected results have occurred.

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Beneﬁts of a unit test ▪ Find problems early. ▪ Facilitate refactoring. ▪ Simplify integration. ▪ Document code usage.

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Types of Android unit test ▪ Instrumented unit test ▪ Local unit test

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Instrumented unit test ▪ Runs on device or emulator ▪ Actually affects the device

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Local unit test ▪ Runs on JVM ▪ No need for device or emulator ▪ Faster than instrumented unit test

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Android Unit Testing Tools & Framework ● JUnit ● Mockito ● PowerMock ● Robolectric ● Espresso ● UI Automator

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JUnit Gradle - testImplementation 'junit:junit:4.12'

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JUnit Annotations @Test @Before @After @BeforeClass @AfterClass @Ignore

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JUnit statement assertions assertFalse(condition) assertEquals(expected, actual, tolerance) assertNull(object) assertNotNull(object) assertSame(expected, actual)

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Mockito “ Objects pre-programmed with expectations which form a speciﬁcation of the calls they are expected to receive.

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Mocking reasons Reason - Your Object have external dependencies Mockito is a Java framework allowing the creation of test mock objects in automated unit tests dependencies { testImplementation "org.mockito:mockito-core:2.11.0" }

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Mockito features ▪ Mocking ▪ Stubbing ▪ Argument matchers ▪ Verifying number of invocations ▪ Verifying order of invocations

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Mockito limitations ▪ Cannot mock ﬁnal classes ▪ Cannot mock static methods ▪ Cannot mock ﬁnal methods ▪ Cannot mock equals(), hashCode()

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PowerMock PowerMock is a framework that extends other mock libraries such as Mockito with more powerful capabilities. Enable mocking of static methods, constructors, ﬁnal classes and methods, private methods, removal of static initializers and more.

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PowerMock testImplementation 'org.powermock:powermock-module-junit4:1.6.4' testImplementation 'org.powermock:powermock-module-junit4-rule:1.6.4' testImplementation 'org.powermock:powermock-api-mockito:1.6.4' testImplementation 'org.powermock:powermock-classloading-xstream:1.6.4'

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Robolectric Unit Testing framework which allows Android application to be tested on JVM without an emulator or device. Robolectric provides implementation of Android SDKs by rewriting Android core libraries using shadow classes

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Robolectric Gradle - testImplementation “org.robolectric:robolectric:latestVersion” Robolectric handles inflation of views, resource loading, and lots of other stuff that’s implemented in native C code on Android devices. **Robolectric is not an integration test framework, i.e., you cannot not test the interaction of Android components with it.

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Writing Testable Code Or how not to lose your mind coding

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Writing Tests can be hard!

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When done right, results in a clean, easy to maintain codebase

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Good Unit Test ● Easy to write ● Readable ● Reliable ● Fast ● Truly Unit

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Testable Code

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Deterministic

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Can you guess why this code is non deterministic?

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Side Effects

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Solution?

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Higher order functions

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Rule of Thumb ● Write deterministic code ● Minimize side effects ● In essence, write pure functions Can impurity really be removed? ● As much as possible, extract it out and keep it contained

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Red Flags ● Static properties and Fields

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Red Flags ● Singletons

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Red Flags ● Static Methods

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What is TDD Test-driven development (TDD) is an approach for software development where you write tests ﬁrst, then use those tests to drive the design and development of your software application.

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TDD Cycle Red — think about what you want to develop Green — think about how to make your tests pass Refactor — think about how to improve your existing implementation

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DEMO

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References Github Link - https://github.com/Niharika8059/UnitTesting-MVVM-Kotlin-Coroutines- Sample Medium link - https://medium.com/1mgofficial/unit-testing-in-mvvm-kotlin-databinding -ba3d4ea08f0e

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Resources https://semaphoreci.com/community/tutorials/stubbing-and-mocking-with-moc kito-2-and-junit https://android.jlelse.eu/better-testing-with-mvvm-ae74d4d872bd https://medium.com/mindorks/unit-testing-for-viewmodel-19f4d76b20d4

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“Writing a test is simple, but writing a code that can be tested is not so simple”

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QUESTIONS?