server-test-host: Rethrown exception in StatusPages exception handler fails test

[juggernaut0]

Ktor Version and Engine Used (client or server and name)
Using ktor server 1.3.1, with ktor-server-test-host

Describe the bug
When using the StatusPages feature to handle exceptions, a rethrowing the exception will bubble out to the test and cause a failure even if it was successfully handled with a call.respond. Rethrowing exceptions is suggested as a way to log caught exceptions in the documentation: https://ktor.io/servers/features/status-pages.html#logging-exceptions

To Reproduce

    @Test
    fun test() {
        open class MyException : RuntimeException()

        withTestApplication({
            install(StatusPages) {
                exception<MyException> {
                    call.respond(HttpStatusCode.UnprocessableEntity, it.toString())
                    throw it // Comment out this line to pass test, but not log exception
                }
            }
            routing {
                get("/") {
                    throw MyException()
                }
            }
        }) {
            with(handleRequest {
                method = HttpMethod.Get
                uri = "/"
            }) {
                assertEquals(HttpStatusCode.UnprocessableEntity, response.status())
            }
        }
    }

Expected behavior
I expect the above test to pass, and the exception to be logged as it would in a non-test application

[cy6erGn0m]

This is by design behaviour: uncaught exceptions are always treated as errors and should not occur.

[juggernaut0]

Okay that makes sense. Perhaps a note should be added to the documentation about that.

[cab404]

This is by design behaviour: uncaught exceptions are always treated as errors and should not occur.

As good as it sounds, that doesn't help us testing.
Is there any way of handling those exceptions (probably in routing?), so we can test error messages?

For now I plan to add wrap each lambda I give to routing into try-catch, but that's obviously a hack.

[e5l]

Hi @cab404, to do that you can add the pipeline interceptor and wrap the proceed method with a try catch block.

[RyanGrif]

Just encountered this myself, and found that you can also get around it by just logging the exception manually, rather than re-throwing it:

    @Test
    fun test() {
        val logger = KotlinLogging.logger {}

        open class MyException : RuntimeException()

        withTestApplication({
            install(StatusPages) {
                exception<MyException> {
                    logger.error(it)
                    call.respond(HttpStatusCode.UnprocessableEntity, it.toString())
                }
            }
            routing {
                get("/") {
                    throw MyException()
                }
            }
        }) {
            with(handleRequest {
                method = HttpMethod.Get
                uri = "/"
            }) {
                assertEquals(HttpStatusCode.UnprocessableEntity, response.status())
            }
        }
    }