Test expected exceptions in Kotlin

Question

In Java, the programmer can specify expected exceptions for JUnit test cases like this:

@Test(expected = ArithmeticException.class)
public void omg()
{
    int bl         


        

Answer 1

Firt steps is to add (expected = YourException::class) in test annotation

@Test(expected = YourException::class)

Second step is to add this function

private fun throwException(): Boolean = throw YourException()

Finally you will have something like this:

@Test(expected = ArithmeticException::class)
fun `get query error from assets`() {
    //Given
    val error = "ArithmeticException"

    //When
    throwException()
    val result =  omg()

    //Then
    Assert.assertEquals(result, error)
}
private fun throwException(): Boolean = throw ArithmeticException()

Answer 2

org.junit.jupiter.api.Assertions.kt

/**
 * Example usage:
 * ```kotlin
 * val exception = assertThrows<IllegalArgumentException>("Should throw an Exception") {
 *     throw IllegalArgumentException("Talk to a duck")
 * }
 * assertEquals("Talk to a duck", exception.message)
 * ```
 * @see Assertions.assertThrows
 */
inline fun <reified T : Throwable> assertThrows(message: String, noinline executable: () -> Unit): T =
        assertThrows({ message }, executable)

Answer 3

Another version of syntaxis using kluent:

@Test
fun `should throw ArithmeticException`() {
    invoking {
        val backHole = 1 / 0
    } `should throw` ArithmeticException::class
}

Answer 4

You can also use generics with kotlin.test package:

import kotlin.test.assertFailsWith 

@Test
fun testFunction() {
    assertFailsWith<MyException> {
         // The code that will throw MyException
    }
}

Answer 5

You can use @Test(expected = ArithmeticException::class) or even better one of Kotlin's library methods like failsWith().

You can make it even shorter by using reified generics and a helper method like this:

inline fun <reified T : Throwable> failsWithX(noinline block: () -> Any) {
    kotlin.test.failsWith(javaClass<T>(), block)
}

And example using the annotation:

@Test(expected = ArithmeticException::class)
fun omg() {

}