为什么不 println!在 Rust 单元测试中工作? [英] Why doesn't println! work in Rust unit tests?
问题描述
我已经实现了以下方法和单元测试:
I've implemented the following method and unit test:
use std::fs::File;
use std::path::Path;
use std::io::prelude::*;
fn read_file(path: &Path) {
let mut file = File::open(path).unwrap();
let mut contents = String::new();
file.read_to_string(&mut contents).unwrap();
println!("{}", contents);
}
#[test]
fn test_read_file() {
let path = &Path::new("/etc/hosts");
println!("{:?}", path);
read_file(path);
}
我以这种方式运行单元测试:
I run the unit test this way:
rustc --test app.rs; ./app
我也可以用
cargo test
我收到一条消息,说测试通过了,但 println!
从未显示在屏幕上.为什么不呢?
I get a message back saying the test passed but the println!
is never displayed on screen. Why not?
推荐答案
发生这种情况是因为 Rust 测试程序隐藏了成功测试的标准输出,以便测试输出整洁.您可以通过将 --nocapture
选项传递给测试二进制文件或 cargo test
来禁用此行为:
This happens because Rust test programs hide the stdout of successful tests in order for the test output to be tidy. You can disable this behavior by passing the --nocapture
option to the test binary or to cargo test
:
#[test]
fn test() {
println!("Hidden output")
}
调用测试:
% rustc --test main.rs; ./main
running 1 test
test test ... ok
test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured
% ./main --nocapture
running 1 test
Hidden output
test test ... ok
test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured
% cargo test -- --nocapture
running 1 test
Hidden output
test test ... ok
test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured
但是,如果测试失败,无论此选项是否存在,都将打印其标准输出.
If tests fail, however, their stdout will be printed regardless if this option is present or not.
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