Kotlin
Summary - Testing
Combine @Test, assertions and MockK to write a calculator test.
Summary - Testing
In this group you learned the JUnit framework, the @Test annotation, the assertEquals/assertTrue assertions, the @BeforeEach/@AfterEach setup/teardown and mocking with MockK.
Now you will combine them: add both add and multiply to Calculator and test with two assertions, then mock a dependency with the fake service pattern. This structure is the foundation of writing reliable tests in Kotlin. Later, property-based testing and integration tests will build on it.
Exercise Test add and multiply
Define class Calculator; inside it add fun add(a: Int, b: Int): Int = a + b and fun multiply(a: Int, b: Int): Int = a * b. Then define a helper fun assertEquals(expected: Int, actual: Int, label: String). In main create val c = Calculator(); call assertEquals(5, c.add(2, 3), "add") and assertEquals(12, c.multiply(3, 4), "multiply"); print println("all passed").
Show example solution
fun main() {
val c = Calculator()
assertEquals(5, c.add(2, 3), "add")
assertEquals(12, c.multiply(3, 4), "multiply")
println("all passed")
}
Exercise The fake Greeter pattern
Define interface Greeter; inside it add fun greet(name: String): String. Define class FakeGreeter : Greeter whose greet body returns "Hello, $name!". Define class App(private val greeter: Greeter) whose fun run(name: String): String body returns greeter.greet(name). In main create val app = App(FakeGreeter()); print println(app.run("Alex")).
Show example solution
interface Greeter {
fun greet(name: String): String
}
class FakeGreeter : Greeter {
override fun greet(name: String): String = "Hello, $name!"
}
class App(private val greeter: Greeter) {
fun run(name: String): String = greeter.greet(name)
}
fun main() {
val app = App(FakeGreeter())
println(app.run("Alex"))
}
Test yourself
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Which is a test annotation?
Show answer
@Test — @Test is JUnit's test method annotation.
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Match the testing concepts
- JUnit
- Test framework
- @Test
- Test method
- assertEquals
- Equality check
- MockK
- Mocking
Next lesson: Project design
