JUnit
- Kotlin course
- Intermediate
- Lesson 106/116
- 5 min
Learn the JUnit 5 test framework.
JUnit: Test framework
JUnit is the most common test framework for the JVM. Kotlin tests use JUnit 5 (Jupiter). The framework is added in build.gradle.kts with the testImplementation("org.jetbrains.kotlin:kotlin-test") dependency. Test classes go in the src/test/kotlin directory.
class CalculatorTest {
@Test
fun adds() {
// assert
}
}Here CalculatorTest is a test class; each test method is marked with @Test. JUnit finds these methods and runs them in turn. A method that completes without throwing counts as a passing test. Tests are run from the IDE or with ./gradlew test.
The test class structure
A test class is a normal Kotlin class; its name usually ends with Test. Inside it each test is written as a method, marked with the @Test annotation. Methods return Unit and take no parameters.
class CalculatorTest {
@Test
fun adds() { }
@Test
fun subtracts() { }
}Here there are two test methods. JUnit runs each separately. Ending the class name with Test is a convention, not a rule; it helps separate test code from production code. Test method names usually reflect the behavior being tested.
Practice Define a Calculator class
Define class Calculator; inside it add fun add(a: Int, b: Int): Int = a + b. In main create an instance with val c = Calculator(); print the result with println(c.add(2, 3)). This class will be tested in later lessons.
Starter code
// Define a Calculator class: add(a: Int, b: Int): Int = a + b
// main: create a Calculator instance, println the result of add(2, 3)
fun main() {
// write here
}Sample solution
class Calculator {
fun add(a: Int, b: Int): Int = a + b
}
fun main() {
val c = Calculator()
println(c.add(2, 3))
}Expected output
5
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What kind of framework is JUnit?
- A test framework Correct answer
- A build tool
- A database
- A UI library
Explanation: JUnit is a test framework for the JVM.
2 Complete the test class name
class Calculator____ {
@Test
fun adds() { }
}class CalculatorTest {
@Test
fun adds() { }
}Explanation: CalculatorTest follows the test class naming convention.
3 Match the JUnit concepts
| Term | Meaning |
|---|---|
JUnit |
Test framework |
@Test |
Test method annotation |
CalculatorTest |
Test class |
src/test/kotlin |
Test directory |