verification that a thread pool executor wont expire threads mid schedule or otherwise run out of threads.

ScheduledThreadPoolExecutor.kt

    @Test fun `when using thread pool executors should keep threads alive for new jobs`(){

        var callCount = 0;

        val executor = ScheduledThreadPoolExecutor(1).apply {
            setKeepAliveTime(1, TimeUnit.MILLISECONDS)
            allowCoreThreadTimeOut(true)
        }
        System.gc()
        
        executor.schedule({ callCount += 1 }, 5, TimeUnit.MILLISECONDS) 

        Thread.sleep(10)
        System.gc()

        executor.schedule({ callCount += 1 }, 5, TimeUnit.MILLISECONDS)
        
        Thread.sleep(10)
        System.gc()

        assertThat(callCount).isEqualTo(2)
    }