The unit test test_shrink make no sense #114
Description
In the test_shrink, if comment the function call pool.set_num_threads(TEST_TASKS); , the test also can pass. Because after_shrink_size == TEST_TASKS and active threads == TEST_TASKS.
Then I want to try write a test case that can test shrink, but it will test fail sometimes (because the implementation in lib.rs).
The code is as follows, test_no_shrink is for the origin test case I metion above, test_shrink_in_sleep is my custom test case using sleep.
#[cfg(test)]
mod test {
use std::{
sync::{Arc, Barrier},
thread::sleep,
time::Duration,
};
use threadpool::ThreadPool;
const TEST_TASKS: usize = 4;
#[test]
fn test_no_shrink() {
let test_tasks_begin = TEST_TASKS + 2;
let pool = ThreadPool::new(test_tasks_begin);
let b0 = Arc::new(Barrier::new(test_tasks_begin + 1));
let b1 = Arc::new(Barrier::new(test_tasks_begin + 1));
for _ in 0..test_tasks_begin {
let (b0, b1) = (b0.clone(), b1.clone());
pool.execute(move || {
b0.wait();
b1.wait();
});
}
let b2 = Arc::new(Barrier::new(TEST_TASKS + 1));
let b3 = Arc::new(Barrier::new(TEST_TASKS + 1));
for _ in 0..TEST_TASKS {
let (b2, b3) = (b2.clone(), b3.clone());
pool.execute(move || {
b2.wait();
b3.wait();
});
}
b0.wait();
// no shrink call, it also can test successfully
// pool.set_num_threads(TEST_TASKS);
assert_eq!(pool.active_count(), test_tasks_begin);
b1.wait();
b2.wait();
assert_eq!(pool.active_count(), TEST_TASKS);
b3.wait();
}
#[test]
fn test_shrink_in_sleep() {
let test_tasks_begin = TEST_TASKS / 2;
let shrink_tasks = 1;
let mut pool = ThreadPool::new(test_tasks_begin);
for _ in 0..TEST_TASKS {
pool.execute(move || {
sleep(Duration::from_secs(1));
})
}
sleep(Duration::from_millis(100));
pool.set_num_threads(shrink_tasks);
/*
* if TEST_TASKS = 4:
*
* time tasks
* [0-1] task0, task1
* [1-2] task2
* [2-3] task3
*/
sleep(Duration::from_secs(1));
assert_eq!(pool.active_count(), 1);
}
}This is the test result:
running 2 tests
test test::test_no_shrink ... ok
test test::test_shrink_in_sleep ... FAILED
failures:
---- test::test_shrink_in_sleep stdout ----
thread 'test::test_shrink_in_sleep' panicked at 'assertion failed: `(left == right)`
left: `2`,
right: `1`', src/main.rs:77:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
failures:
test::test_shrink_in_sleep
test result: FAILED. 1 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 1.10sAlthough I know the thread pool does not need such a precise shrink, I want to ask how to write a test case to test whether the shrink really works and the test case can pass everytime.