How do I test expected Unchecked Exceptions in Kotlin?

Question

I am trying to write a test in Kotlin that makes sure an unchecked exception is thrown in specific circumstances.

I am trying to use org.junit.jupiter.api.Assertions.assertThrows like this:

assertThrows(MyRuntimeException::class, Executable { myMethodThatThrowsThatException() })

when i try this i get a

Type inference failed compiler error

because my Exception in not a CheckedException but a RuntimeException. Is there any good way to test this behavior without doing the naive try catch?

score 7 · Accepted Answer · answered Feb 15 '18 at 17:01

7

You can use assertFailsWith from the Kotlin standard library:

assertFailsWith<MyRuntimeException> { myMethodThatThrowsThatException() }

answered Feb 15 '18 at 17:01

yole

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score 4 · Answer 2 · answered Feb 15 '18 at 16:59

The assertThrows method expects a Class as its first parameter, but you're trying to give it a KClass. To fix this, just do the following (as described in the documentation here):

assertThrows(MyRuntimeException::class.java, Executable { myMethodThatThrowsThatException() })

You can also leave out the explicit Executable type:

assertThrows(MyRuntimeException::class.java, { myMethodThatThrowsThatException() })

Or if your method really doesn't take any parameters, you can use a method reference to it:

assertThrows(MyRuntimeException::class.java, ::myMethodThatThrowsThatException)

How do I test expected Unchecked Exceptions in Kotlin?

2 Answers2