Unit Testing in Kotlin

Unit Testing in Kotlin Egor Andreevici Software Developer @ 1&1 @EgorAnd

Java Kotlin + Official + Stable - Old - Verbose + Modern + Expressive - Stable? - Support?

Starting with Kotlin on Android? Start small! Start with unit tests!

Benefits of Unit Tests Provide a safety net around your code Document your code… what? Promote good design practices

Bad Documentation /** * Get a subview of the root view at a certain position. * * @param position Position, 0 <= position < root child count * @return Subview at given position, or {@code null} if position is out of * bounds */ public View getViewAtPosition(int position) { if (position >= 0 && position < root.getChildCount()) { return root.getChildAt(position); } return null; }

Bad Documentation /** * Get a subview of the root view at a certain position. * * @param position Position, 0 <= position < root child count * @return Subview at given position, or {@code null} if position is out of * bounds */ public View getViewAtPosition(int position) { if (position >= 0 && position < root.getChildCount()) { return root.getChildAt(position); } throw new IndexOutOfBoundsException("Invalid position " + position); }

A Better Test @Test public void shouldReturnNullIfCalledWithInvalidPosition() { doReturn(0).when(mockParent).getChildCount(); assertThat(docs.getViewAtPosition(0)).isNull(); }

Kotlinize @Test fun shouldReturnNullIfCalledWithInvalidPosition() { doReturn(0).`when`<ViewGroup>(mockParent).childCount assertThat(docs.getViewAtPosition(0)).isNull() }

Better Method Names @Test fun `Should return null if called with invalid position`() { doReturn(0).`when`<ViewGroup>(mockParent).childCount assertThat(docs.getViewAtPosition(0)).isNull() }

Better Mocking with Mockito-Kotlin ● Reified types for mock creation ● Fluent method mocking syntax ● More niceties

Better Mocking with Mockito-Kotlin private var mockParent = mock<ViewGroup>()

Better Mocking with Mockito-Kotlin // private var mockParent = mock<ViewGroup>() private var mockParent: ViewGroup = mock { on { childCount } doReturn 0 }

Better Mocking with Mockito-Kotlin @Test fun `Should return null if called with invalid position`() { whenever(mockParent.childCount) doReturn 0 assertThat(docs.getViewAtPosition(0)).isNull() }

How Does It Work? inline fun <reified T : Any> mock(): T = Mockito.mock(T::class.java)

Better Assertions with Kluent @Test fun `Should return null if called with invalid position`() { whenever(mockParent.childCount) doReturn 0 docs.getViewAtPosition(0) `should be` null }

How Does It Work? import org.junit.Assert.* infix fun Any?.`should be`(theOther: Any?) = assertSame(theOther, this) infix fun Any?.shouldBe(theOther: Any?) = this `should be` theOther

Multiline Strings val json = """ { "name": "Bob", "age": 57 } """ @Test fun `Should parse JSON correctly`() { gson.fromJson(json, Person::class.java) `should equal` Person("Bob", 57) }

“with” for Multiple Assertions @Test fun `Should parse JSON correctly #2`() { val person = gson.fromJson(json, Person::class.java) with(person) { name `should equal` "Bob" age `should equal` 57 } }

Factory Functions with Named Args public class Person { private String name; private int age; private boolean isAKotlinProgrammer; public Person(String name, int age, boolean isAKotlinProgrammer) { this.name = name; this.age = age; this.isAKotlinProgrammer = isAKotlinProgrammer; } … }

Factory Functions with Named Args fun person( name: String = "", age: Int = 0, isAKotlinProgrammer: Boolean = false) = Person(name, age, isAKotlinProgrammer) @Test fun `Should ...`() { val person = person(name = "Bob", age = 57) ... }

@JvmOverloads @JvmOverloads fun person( name: String = "", age: Int = 0, isAKotlinProgrammer: Boolean = false) = Person(name, age, isAKotlinProgrammer)

Thanks! Egor Andreevici Software Developer @ 1&1 @EgorAnd

Unit Testing in Kotlin

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