Unit Testing- What, Why and How?

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Unit Testing: What, Why and How? Niharika Arora Senior Software Engineer, 1mg

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Agenda ● Why Tests?

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Agenda ● Why Tests? ● Tools and Frameworks

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Agenda ● Why Tests? ● Tools and Frameworks ● Demo

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Agenda ● Why Tests? ● Tools and Frameworks ● Demo ● Writing Testable Code

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● “Mobile apps are frontend apps, the real logic is in the backend, so backend apps should be tested instead.”

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● “Mobile apps are frontend apps, the real logic is in the backend, so backend apps should be tested instead.” ● “Mobile apps are difficult to unit test, because most of the logic is done in the UI. At most, you should only care about UI tests.” ● “Mobile apps are “simple” or “tiny” compared to backend apps. Thus, effort should be put in the features instead of wasting time making tests.”

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Why test?

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Why test? ● No recurring cost of doing ﬁxes when things break in production.

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Why test? ● No recurring cost of doing ﬁxes when things break in production. ● Maintenance and Refactoring becomes easy.

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Why test? ● No recurring cost of doing ﬁxes when things break in production. ● Maintenance and Refactoring becomes easy. ● Validating your changes.

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Why test? ● No recurring cost of doing ﬁxes when things break in production. ● Maintenance and Refactoring becomes easy. ● Validating your changes. ● Debugging

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Why test? ● No recurring cost of doing ﬁxes when things break in production. ● Maintenance and Refactoring becomes easy. ● Validating your changes. ● Debugging ● Simplify integration.

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Why test? ● No recurring cost of doing ﬁxes when things break in production. ● Maintenance and Refactoring becomes easy. ● Validating your changes. ● Debugging ● Simplify integration. ● The list never ends.

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Testing Pyramid

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UI Tests

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UI Tests ● Interact with the UI of your app, they emulate the user behavior and assert UI results.

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UI Tests ● Interact with the UI of your app, they emulate the user behavior and assert UI results. ● Slowest and most expensive tests as they require a device/emulator to run.

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UI Tests ● Interact with the UI of your app, they emulate the user behavior and assert UI results. ● Slowest and most expensive tests as they require a device/emulator to run. ● Tools : Espresso and UI Automator

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Integration Tests

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Integration Tests ● When we need to check how our code interacts with other parts of the Android framework but without the complexity of the UI.

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Integration Tests ● How your code interacts with other parts of the Android framework but without the complexity of the UI. ● Don’t require a device/emulator to run

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Integration Tests ● How your code interacts with other parts of the Android framework but without the complexity of the UI. ● Don’t require a device/emulator to run ● Tools: Roboelectric.

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Unit Test

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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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Unit Test ● Fastest and least expensive tests as they don’t require a device/emulator to run.

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Unit Test ● Fastest and least expensive tests as they don’t require a device/emulator to run. ● Testing one logical unit/component guarantee that our component works properly for the set of inputs that we expect.

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Good rule of Thumb

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Anatomy of a unit test

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Anatomy of a unit test ▪ Arrange all necessary preconditions and inputs.

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Anatomy of a unit test ▪ Arrange all necessary preconditions and inputs. ▪ Act on the object or method under test.

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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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Android Unit Testing Tools & Frameworks

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Android Unit Testing Tools & Framework ● JUnit

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JUnit

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JUnit ● Testing a class/method that doesn't call Android APIs.

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JUnit ● Testing a class/method that doesn't call Android APIs. ● Assertion-based testing

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

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

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JUnit Limitations

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JUnit Limitations ● Your Object/class have external dependencies

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Android Unit Testing Tools & Framework ● JUnit ● Mockito

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Mockito “ A Java framework allowing the creation of test mock objects in automated unit tests .

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Mockito features ▪ Mocking

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@Mock private lateinit var loginModel: LoginModel

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Mockito features ▪ Mocking ▪ Stubbing

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`when`(UtilityClass.isNetworkConnected()).thenReturn(true)

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Mockito features ▪ Mocking ▪ Stubbing ▪ Argument matchers

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`when`(UtilityClass.isEmailValid(ArgumentMatchers.anyString())).thenReturn(true)

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

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

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Mockito limitations

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Mockito limitations ▪ Cannot mock ﬁnal classes

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Mockito limitations ▪ Cannot mock ﬁnal classes ▪ Cannot mock static methods

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Mockito limitations ▪ Cannot mock ﬁnal classes ▪ Cannot mock static methods ▪ Cannot mock ﬁnal methods

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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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Android Unit Testing Tools & Framework ● JUnit ● Mockito ● PowerMock

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PowerMock

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PowerMock ● Framework that extends other mock libraries such as Mockito with more powerful capabilities.

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PowerMock ● 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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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

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Good Unit Test ● Easy to write

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Good Unit Test ● Easy to write ● Readable

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Good Unit Test ● Easy to write ● Readable ● Reliable

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

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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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Deterministic

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Can you guess why this code is non deterministic?

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Side Effects

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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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Rule of Thumb

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

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References Github Link - https://github.com/niharika2810/UnitTesting-MVVM-Kotlin-Koin-Coroutines-Sa mple Medium link - https://thedroidlady.com/2019/07/10/unit-testing-in-mvvm-kotlin-databinding.ht ml

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Resources https://android.jlelse.eu/better-testing-with-mvvm-ae74d4d872bd https://blog.mindorks.com/mockito-cannot-mock-in-kotlin https://blog.mindorks.com/using-mockito-in-android-unit-testing-as- a-pro https://www.raywenderlich.com/195-android-unit-testing-with-mockit o https://medium.com/@mohitaunni/tdd-in-andoid-a-brief-story-part-1- 22166d211750

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Let’s connect ● LinkedIn : https://www.linkedin.com/in/thedroidlady/ ● Medium : https://medium.com/@nik.arora8059 ● Github : https://github.com/niharika2810 ● Twitter : https://twitter.com/theDroidLady ● Personal : https://thedroidlady.com/

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