Class to test

inline fun completable(
        crossinline action: () -> Unit,
        crossinline finally: () -> Unit
): Completable {
    return Completable.create { emitter ->
        try {
            action()
            emitter.onComplete()
        } catch (t: Throwable) {
            // Attempts to emit the specified {@code Throwable} error if the downstream
            // hasn't cancelled the sequence or is otherwise terminated, returning false
            // if the emission is not allowed to happen due to lifecycle restrictions.
            // <p>
            // Unlike {@link #onError(Throwable)}, the {@code RxJavaPlugins.onError} is not called
            // if the error could not be delivered.
            emitter.tryOnError(t)
        } finally {
            finally()
        }
    }
}

Test

@Test
fun `Completable do not crash when terminated`() {
    var ex: Throwable? = null
    RxJavaPlugins.setErrorHandler { t -> ex = t }

    Completable.mergeArray(
            completable {
                throw IOException("test1")
            }.subscribeOn(Schedulers.io()),
            completable {
                throw IOException("test2")
            }.subscribeOn(Schedulers.io())
    ).onErrorComplete()
            .blockingAwait()

    RxJavaPlugins.setErrorHandler(null)

    ex?.let {
        throw it
    }
}