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< h1 id = "编写测试及控制执行" > < a class = "header" href = "#编写测试及控制执行" > 编写测试及控制执行< / a > < / h1 >
< p > 在 Rust 中，测试是通过函数的方式实现的，它可以用于验证被测试代码的正确性。测试函数往往依次执行以下三种行为：< / p >
< ol >
< li > 设置所需的数据或状态< / li >
< li > 运行想要测试的代码< / li >
< li > 判断( assert )返回的结果是否符合预期< / li >
< / ol >
< p > 让我们来看看该如何使用 Rust 提供的特性来按照上述步骤编写测试用例。< / p >
< h2 id = "测试函数" > < a class = "header" href = "#测试函数" > 测试函数< / a > < / h2 >
< p > 当使用 < code > Cargo< / code > 创建一个 < code > lib< / code > 类型的包时，它会为我们自动生成一个测试模块。先来创建一个 < code > lib< / code > 类型的 < code > adder< / code > 包：< / p >
< pre > < code class = "language-shell" > $ cargo new adder --lib
Created library `adder` project
$ cd adder
< / code > < / pre >
< p > 创建成功后，在 < em > src/lib.rs< / em > 文件中可以发现如下代码:< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > #[cfg(test)]
mod tests {
#[test]
fn it_works() {
assert_eq!(2 + 2, 4);
}
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 其中，< code > tests< / code > 就是一个测试模块，< code > it_works< / code > 则是我们的主角：测试函数。< / p >
< p > 可以看出，测试函数需要使用 < code > test< / code > 属性进行标注。关于属性( < code > attribute< / code > )，我们在之前的章节已经见过类似的 < code > derive< / code > ，使用它可以派生自动实现的 < code > Debug< / code > 、< code > Copy< / code > 等特征，同样的，使用 < code > test< / code > 属性，我们也可以获取 Rust 提供的测试特性。< / p >
< p > 经过 < code > test< / code > 标记的函数就可以被测试执行器发现，并进行运行。当然，在测试模块 < code > tests< / code > 中，还可以定义非测试函数，这些函数可以用于设置环境或执行一些通用操作：例如为部分测试函数提供某个通用的功能，这种功能就可以抽象为一个非测试函数。< / p >
< p > 换而言之，正是因为测试模块既可以定义测试函数又可以定义非测试函数，导致了我们必须提供一个特殊的标记 < code > test< / code > ，用于告知哪个函数才是测试函数。< / p >
< h4 id = "assert_eq" > < a class = "header" href = "#assert_eq" > assert_eq< / a > < / h4 >
< p > 在测试函数中，还使用到了一个内置的断言：< code > assert_eq< / code > ，该宏用于对结果进行断言：< code > 2 + 2< / code > 是否等于 < code > 4< / code > 。与之类似， < a href = "https://course.rs/test/assertion.html" > 后续章节< / a > 。< / p >
< h2 id = "cargo-test" > < a class = "header" href = "#cargo-test" > cargo test< / a > < / h2 >
< p > 下面使用 < code > cargo test< / code > 命令来运行项目中的所有测试:< / p >
< pre > < code class = "language-shell" > $ cargo test
Compiling adder v0.1.0 (file:///projects/adder)
Finished test [unoptimized + debuginfo] target(s) in 0.57s
Running unittests (target/debug/deps/adder-92948b65e88960b4)
running 1 test
test tests::it_works ... ok
test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
Doc-tests adder
running 0 tests
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
< / code > < / pre >
< p > 上面测试输出中，有几点值得注意:< / p >
< ul >
< li > 测试用例是分批执行的，< code > running 1 test< / code > 表示下面的输出 < code > test result< / code > 来自一个测试用例的运行结果。< / li >
< li > < code > test tests::it_works< / code > 中包含了测试用例的名称< / li >
< li > < code > test result: ok< / code > 中的 < code > ok< / code > 表示测试成功通过< / li >
< li > < code > 1 passed< / code > 代表成功通过一个测试用例(因为只有一个)， < code > 0 failed< / code > : 没有测试用例失败，< code > 0 ignored< / code > 说明我们没有将任何测试函数标记为运行时可忽略，< code > 0 filtered< / code > 意味着没有对测试结果做任何过滤，< code > 0 measured< / code > 代表< a href = "https://course.rs/test/benchmark.html" > 基准测试(benchmark)< / a > 的结果< / li >
< / ul >
< p > 关于 < code > filtered< / code > 和 < code > ignored< / code > 的使用，在本章节的后续内容我们会讲到，这里暂且略过。< / p >
< p > 还有一个很重要的点，输出中的 < code > Doc-tests adder< / code > 代表了文档测试，由于我们的代码中没有任何文档测试的内容，因此这里的测试用例数为 < code > 0< / code > ，关于文档测试的详细介绍请参见< a href = "https://course.rs/basic/comment.html#文档注释" > 这里< / a > 。< / p >
< p > 大家还可以尝试修改下测试函数的名称，例如修改为 < code > exploration< / code > ，看看运行结果将如何变化。< / p >
< h4 id = "失败的测试用例" > < a class = "header" href = "#失败的测试用例" > 失败的测试用例< / a > < / h4 >
< p > 是时候开始写自己的测试函数了，为了演示，这次我们来写一个会运行失败的:< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > #[cfg(test)]
mod tests {
#[test]
fn exploration() {
assert_eq!(2 + 2, 4);
}
#[test]
fn another() {
panic!("Make this test fail");
}
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 新的测试函数 < code > another< / code > 相当简单粗暴，直接使用 < code > panic< / code > 来报错，使用 < code > cargo test< / code > 运行看看结果：< / p >
< pre > < code class = "language-shell" > running 2 tests
test tests::another ... FAILED
test tests::exploration ... ok
failures:
---- tests::another stdout ----
thread 'main' panicked at 'Make this test fail', src/lib.rs:10:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
failures:
tests::another
test result: FAILED. 1 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
error: test failed, to rerun pass '--lib'
< / code > < / pre >
< p > 从结果看，两个测试函数，一个成功，一个失败，同时在输出中准确的告知了失败的函数名: < code > failures: tests::another< / code > ，同时还给出了具体的失败原因： < code > tests::another stdout< / code > 。这两者虽然看起来存在重复，但是前者用于说明每个失败的具体原因，后者用于给出一眼可得结论的汇总信息。< / p >
< p > 有同学可能会好奇，这两个测试函数以什么方式运行？ 它们会运行在同一个线程中吗？ ， < code > main< / code > 发现有一个测试线程死掉时，< code > main< / code > 会将相应的测试标记为失败。< / p >
< p > 事实上，多线程运行测试虽然性能高，但是存在数据竞争的风险，在后文我们会对其进行详细介绍并给出解决方案。< / p >
< h2 id = "自定义失败信息" > < a class = "header" href = "#自定义失败信息" > 自定义失败信息< / a > < / h2 >
< p > 默认的失败信息在有时候并不是我们想要的，来看一个例子：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > pub fn greeting(name: & str) -> String {
format!("Hello {}!", name)
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn greeting_contains_name() {
let result = greeting("Sunface");
assert!(result.contains("孙飞"));
}
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 使用 < code > cargo test< / code > 运行后，错误如下：< / p >
< pre > < code class = "language-shell" > test tests::greeting_contains_name ... FAILED
failures:
---- tests::greeting_contains_name stdout ----
thread 'tests::greeting_contains_name' panicked at 'assertion failed: result.contains(\"孙飞\")', src/lib.rs:12:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
failures:
tests::greeting_contains_name
< / code > < / pre >
< p > 可以看出，这段报错除了告诉我们错误发生的地方，并没有更多的信息，那再来看看该如何提供一些更有用的信息：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > fn greeting_contains_name() {
let result = greeting("Sunface");
let target = "孙飞";
assert!(
result.contains(target),
"你的问候中并没有包含目标姓名 {} ，你的问候是 `{}`",
target,
result
);
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 这段代码跟之前并无不同，只是为 < code > assert!< / code > 新增了几个格式化参数，这种使用方式与 < code > format!< / code > 并无区别。再次运行后，输出如下：< / p >
< pre > < code class = "language-shell" > ---- tests::greeting_contains_name stdout ----
thread 'tests::greeting_contains_name' panicked at '你的问候中并没有包含目标姓名 孙飞 ，你的问候是 `Hello Sunface!`', src/lib.rs:14:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
< / code > < / pre >
< p > 这次的报错就清晰太多了，真棒！在测试用例少的时候，也许这种信息还无法体现最大的价值，但是一旦测试多了后，详尽的报错信息将帮助我们更好的进行 Debug。< / p >
< h2 id = "测试-panic" > < a class = "header" href = "#测试-panic" > 测试 panic< / a > < / h2 >
< p > 在之前的例子中，我们通过 < code > panic< / code > 来触发报错，但是如果一个函数本来就会 < code > panic< / code > ，而我们想要检查这种结果呢？< / p >
< p > 也就是说，我们需要一个办法来测试一个函数是否会 < code > panic< / code > ，对此， Rust 提供了 < code > should_panic< / code > 属性注解，和 < code > test< / code > 注解一样，对目标测试函数进行标注即可：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > pub struct Guess {
value: i32,
}
impl Guess {
pub fn new(value: i32) -> Guess {
if value < 1 || value > 100 {
panic!("Guess value must be between 1 and 100, got {}.", value);
}
Guess { value }
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
#[should_panic]
fn greater_than_100() {
Guess::new(200);
}
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 上面是一个简单的猜数字游戏，< code > Guess< / code > 结构体的 < code > new< / code > 方法在传入的值不在 [1,100] 之间时，会直接 < code > panic< / code > ，而在测试函数 < code > greater_than_100< / code > 中，我们传入的值 < code > 200< / code > 显然没有落入该区间，因此 < code > new< / code > 方法会直接 < code > panic< / code > ，为了测试这个预期的 < code > panic< / code > 行为，我们使用 < code > #[should_panic]< / code > 对其进行了标注。< / p >
< pre > < code class = "language-shell" > running 1 test
test tests::greater_than_100 - should panic ... ok
test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
< / code > < / pre >
< p > 从输出可以看出， < code > panic< / code > 的结果被准确的进行了测试，那如果测试函数中的代码不再 < code > panic< / code > 呢？例如：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > fn greater_than_100() {
Guess::new(50);
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 此时显然会测试失败，因为我们预期一个 < code > panic< / code > ，但是 < code > new< / code > 函数顺利的返回了一个 < code > Guess< / code > 实例:< / p >
< pre > < code class = "language-shell" > running 1 test
test tests::greater_than_100 - should panic ... FAILED
failures:
---- tests::greater_than_100 stdout ----
note: test did not panic as expected // 测试并没有按照预期发生 panic
< / code > < / pre >
< h4 id = "expected" > < a class = "header" href = "#expected" > expected< / a > < / h4 >
< p > 虽然 < code > panic< / code > 被成功测试到，但是如果代码发生的 < code > panic< / code > 和我们预期的 < code > panic< / code > 不符合呢？因为一段糟糕的代码可能会在不同的代码行生成不同的 < code > panic< / code > 。< / p >
< p > 鉴于此，我们可以使用可选的参数 < code > expected< / code > 来说明预期的 < code > panic< / code > 长啥样：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > // --snip--
impl Guess {
pub fn new(value: i32) -> Guess {
if value < 1 {
panic!(
"Guess value must be greater than or equal to 1, got {}.",
value
);
} else if value > 100 {
panic!(
"Guess value must be less than or equal to 100, got {}.",
value
);
}
Guess { value }
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
#[should_panic(expected = "Guess value must be less than or equal to 100")]
fn greater_than_100() {
Guess::new(200);
}
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 这段代码会通过测试，因为通过增加了 < code > expected< / code > ，我们成功指定了期望的 < code > panic< / code > 信息，大家可以顺着代码推测下：把 < code > 200< / code > 带入到 < code > new< / code > 函数中看看会触发哪个 < code > panic< / code > 。< / p >
< p > 如果注意看，你会发现 < code > expected< / code > 的字符串和实际 < code > panic< / code > 的字符串可以不同，前者只需要是后者的字符串前缀即可，如果改成 < code > #[should_panic(expected = "Guess value must be less than")]< / code > ，一样可以通过测试。< / p >
< p > 这里由于篇幅有限，我们就不再展示测试失败的报错，大家可以自己修改下 < code > expected< / code > 的信息，然后看看报错后的输出长啥样。< / p >
< h2 id = "使用-resultt-e" > < a class = "header" href = "#使用-resultt-e" > 使用 < code > Result< T, E> < / code > < / a > < / h2 >
< p > 在之前的例子中，< code > panic< / code > 扫清一切障碍，但是它也不是万能的，例如你想在测试中使用 < code > ?< / code > 操作符进行链式调用该怎么办？那就得请出 < code > Result< T, E> < / code > 了：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > #[cfg(test)]
mod tests {
#[test]
fn it_works() -> Result< (), String> {
if 2 + 2 == 4 {
Ok(())
} else {
Err(String::from("two plus two does not equal four"))
}
}
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 如上所示，测试函数不会再使用 < code > assert_eq!< / code > 导致 < code > panic< / code > ，而是手动进行了逻辑判断，并返回一个 < code > Result< / code > 。当然，当这么实现时，< code > #[should_panic]< / code > 将无法再被使用。< / p >
< p > 至此，关于如何写测试的基本知识，大家已经了解的差不多了，下面来看看该如何控制测试的执行。< / p >
< h2 id = "使用----分割命令行参数" > < a class = "header" href = "#使用----分割命令行参数" > 使用 < code > --< / code > 分割命令行参数< / a > < / h2 >
< p > 大家应该都知道 < code > cargo build< / code > 可以将代码编译成一个可执行文件，那你知道 < code > cargo run< / code > 和 < code > cargo test< / code > 是如何运行的吗？其实道理都一样，这两个也是将代码编译成可执行文件，然后进行运行，唯一的区别就在于这个可执行文件随后会被删除。< / p >
< p > 正因为如此，< code > cargo test< / code > 也可以通过命令行参数来控制测试的执行，例如你可以通过参数来让默认的多线程测试变成单线程下的测试。需要注意的是命令行参数有两种，这两种通过 < code > --< / code > 进行分割：< / p >
< ul >
< li > 第一种是提供给 < code > cargo test< / code > 命令本身的，这些参数在 < code > --< / code > 之前指定< / li >
< li > 第二种是提供给编译后的可执行文件的，在 < code > --< / code > 之后指定< / li >
< / ul >
< p > 例如我们可以使用 < code > cargo test --help< / code > 来查看第一种参数的帮助列表，还可以通过 < code > cargo test -- --help< / code > 来查看第二种的帮助列表。< / p >
< p > 先来看看第二种参数中的其中一个，它可以控制测试是并行运行还是顺序运行。< / p >
< h2 id = "测试用例的并行或顺序执行" > < a class = "header" href = "#测试用例的并行或顺序执行" > 测试用例的并行或顺序执行< / a > < / h2 >
< p > 当运行多个测试函数时，默认情况下是为每个测试都生成一个线程，然后通过主线程来等待它们的完成和结果。这种模式的优点很明显，那就是并行运行会让整体测试时间变短很多，运行过大量测试用例的同学都明白并行测试的重要性：生命苦短，我用并行。< / p >
< p > 但是有利就有弊，并行测试最大的问题就在于共享状态的修改，因为你难以控制测试的运行顺序，因此如果多个测试共享一个数据，那么对该数据的使用也将变得不可控制。< / p >
< p > 例如，我们有多个测试，它们每个都会往该文件中写入一些< strong > 自己的数据< / strong > ，最后再从文件中读取这些数据进行对比。由于所有测试都是同时运行的，当测试 < code > A< / code > 写入数据准备读取并对比时，很有可能会被测试 < code > B< / code > 写入新的数据，导致 < code > A< / code > 写入的数据被覆盖，然后 < code > A< / code > 再读取到的就是 < code > B< / code > 写入的数据。结果 < code > A< / code > 测试就会失败，而且这种失败还不是因为测试代码不正确导致的！< / p >
< p > 解决办法也有，我们可以让每个测试写入自己独立的文件中，当然，也可以让所有测试一个接着一个顺序运行:< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > $ cargo test -- --test-threads=1
< span class = "boring" > }< / span > < / code > < / pre >
< p > 首先能注意到的是该命令行参数是第二种类型：提供给编译后的可执行文件的，因为它在 < code > --< / code > 之后进行传递。其次，细心的同学可能会想到，线程数不仅仅可以指定为 < code > 1< / code > ，还可以指定为 < code > 4< / code > 、< code > 8< / code > ，当然，想要顺序运行，就必须是 < code > 1< / code > 。< / p >
< h2 id = "测试函数中的-println" > < a class = "header" href = "#测试函数中的-println" > 测试函数中的 < code > println!< / code > < / a > < / h2 >
< p > 默认情况下，如果测试通过，那写入标准输出的内容是不会显示在测试结果中的:< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > fn prints_and_returns_10(a: i32) -> i32 {
println!("I got the value {}", a);
10
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn this_test_will_pass() {
let value = prints_and_returns_10(4);
assert_eq!(10, value);
}
#[test]
fn this_test_will_fail() {
let value = prints_and_returns_10(8);
assert_eq!(5, value);
}
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 上面代码使用 < code > println!< / code > 输出收到的参数值，来看看测试结果:< / p >
< pre > < code class = "language-shell" > running 2 tests
test tests::this_test_will_fail ... FAILED
test tests::this_test_will_pass ... ok
failures:
---- tests::this_test_will_fail stdout ----
I got the value 8
thread 'main' panicked at 'assertion failed: `(left == right)`
left: `5`,
right: `10`', src/lib.rs:19:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
failures:
tests::this_test_will_fail
test result: FAILED. 1 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
< / code > < / pre >
< p > 大家注意看，< code > I got the value 4< / code > 并没有被输出，因为该测试顺利通过了，如果就是想要看所有的输出，该怎么办呢？< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > $ cargo test -- --show-output
< span class = "boring" > }< / span > < / code > < / pre >
< p > 如上所示，只需要增加一个参数，具体的输出就不再展示，总之这次大家一定可以顺利看到 < code > I got the value 4< / code > 的身影。< / p >
< h2 id = "指定运行一部分测试" > < a class = "header" href = "#指定运行一部分测试" > 指定运行一部分测试< / a > < / h2 >
< p > 在 Mysql 中有上百万的单元测试，如果使用类似 < code > cargo test< / code > 的命令来运行全部的测试，那开发真的工作十分钟，吹牛八小时了。对于 Rust 的中大型项目也一样，每次都运行全部测试是不可接受的，特别是你的工作仅仅是项目中的一部分时。< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > pub fn add_two(a: i32) -> i32 {
a + 2
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn add_two_and_two() {
assert_eq!(4, add_two(2));
}
#[test]
fn add_three_and_two() {
assert_eq!(5, add_two(3));
}
#[test]
fn one_hundred() {
assert_eq!(102, add_two(100));
}
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 如果直接使用 < code > cargo test< / code > 运行，那三个测试函数会同时并行的运行：< / p >
< pre > < code class = "language-shell" > running 3 tests
test tests::add_three_and_two ... ok
test tests::add_two_and_two ... ok
test tests::one_hundred ... ok
test result: ok. 3 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
Doc-tests adder
running 0 tests
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
< / code > < / pre >
< p > 就不说上百万测试，就说几百个，想象一下结果会是怎么样，下面我们来看看该如何解决这个问题。< / p >
< h4 id = "运行单个测试" > < a class = "header" href = "#运行单个测试" > 运行单个测试< / a > < / h4 >
< p > 这个很简单，只需要将指定的测试函数名作为参数即可：< / p >
< pre > < code class = "language-shell" > $ cargo test one_hundred
running 1 test
test tests::one_hundred ... ok
test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 2 filtered out; finished in 0.00s
< / code > < / pre >
< p > 此时，只有测试函数 < code > one_hundred< / code > 会被运行， ， ， ， < code > 2 filtered out< / code > 提示我们：有两个测试函数被过滤了。< / p >
< p > 但是，如果你试图同时指定多个名称，那抱歉:< / p >
< pre > < code class = "language-shell" > $ cargo test one_hundred,add_two_and_two
$ cargo test one_hundred add_two_and_two
< / code > < / pre >
< p > 这两种方式统统不行，此时就需要使用名称过滤的方式来实现了。< / p >
< h4 id = "通过名称来过滤测试" > < a class = "header" href = "#通过名称来过滤测试" > 通过名称来过滤测试< / a > < / h4 >
< p > 我们可以通过指定部分名称的方式来过滤运行相应的测试:< / p >
< pre > < code class = "language-shell" > $ cargo test add
running 2 tests
test tests::add_three_and_two ... ok
test tests::add_two_and_two ... ok
test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 1 filtered out; finished in 0.00s
< / code > < / pre >
< p > 事实上，你不仅可以使用前缀，还能使用名称中间的一部分：< / p >
< pre > < code class = "language-shell" > $ cargo test and
running 2 tests
test tests::add_two_and_two ... ok
test tests::add_three_and_two ... ok
test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 1 filtered out; finished in 0.00s
< / code > < / pre >
< p > 其中还有一点值得注意，那就是测试模块 < code > tests< / code > 的名称也出现在了最终结果中：< code > tests::add_two_and_two< / code > ，这是非常贴心的细节，也意味着我们可以通过< strong > 模块名称来过滤测试< / strong > ： < / p >
< pre > < code class = "language-shell" > $ cargo test tests
running 3 tests
test tests::add_two_and_two ... ok
test tests::add_three_and_two ... ok
test tests::one_hundred ... ok
test result: ok. 3 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
< / code > < / pre >
< h4 id = "忽略部分测试" > < a class = "header" href = "#忽略部分测试" > 忽略部分测试< / a > < / h4 >
< p > 有时候，一些测试会非常耗时间，因此我们希望在 < code > cargo test< / code > 中对它进行忽略，如果使用之前的方式，我们需要将所有需要运行的名称指定一遍，这非常麻烦，好在 Rust 允许通过 < code > ignore< / code > 关键字来忽略特定的测试用例:< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > #[test]
fn it_works() {
assert_eq!(2 + 2, 4);
}
#[test]
#[ignore]
fn expensive_test() {
// 这里的代码需要几十秒甚至几分钟才能完成
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 在这里，我们使用 < code > #[ignore]< / code > 对 < code > expensive_test< / code > 函数进行了标注，看看结果：< / p >
< pre > < code class = "language-shell" > $ cargo test
running 2 tests
test expensive_test ... ignored
test it_works ... ok
test result: ok. 1 passed; 0 failed; 1 ignored; 0 measured; 0 filtered out; finished in 0.00s
Doc-tests adder
running 0 tests
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
< / code > < / pre >
< p > 输出中的 < code > test expensive_test ... ignored< / code > 意味着该测试函数被忽略了，因此并没有被执行。< / p >
< p > 当然，也可以通过以下方式运行被忽略的测试函数：< / p >
< pre > < code class = "language-shell" > $ cargo test -- --ignored
running 1 test
test expensive_test ... ok
test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 1 filtered out; finished in 0.00s
Doc-tests adder
running 0 tests
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
< / code > < / pre >
< h4 id = "组合过滤" > < a class = "header" href = "#组合过滤" > 组合过滤< / a > < / h4 >
< p > 上面的方式虽然很强大，但是单独使用依然存在局限性。好在它们还能组合使用，例如还是之前的代码：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > #[cfg(test)]
mod tests {
use super::*;
#[test]
fn it_works() {
assert_eq!(2 + 2, 4);
}
#[test]
#[ignore]
fn expensive_test() {
// 这里的代码需要几十秒甚至几分钟才能完成
}
#[test]
#[ignore]
fn expensive_run() {
// 这里的代码需要几十秒甚至几分钟才能完成
}
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 然后运行 < code > tests< / code > 模块中的被忽略的测试函数< / p >
< pre > < code class = "language-shell" > $ cargo test tests -- --ignored
running 2 tests
test tests::expensive_test ... ok
test tests::expensive_run ... ok
test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 1 filtered out; finished in 0.00s
< / code > < / pre >
< p > 运行名称中带 < code > run< / code > 且被忽略的测试函数：< / p >
< pre > < code class = "language-shell" > $ cargo test run -- --ignored
running 1 test
test tests::expensive_run ... ok
test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 2 filtered out; finished in 0.00s
< / code > < / pre >
< p > 类似的还有很多，大家可以自己摸索研究下，总之，熟练掌握测试的使用是非常重要的，虽然包括我在内的很多开发并不喜欢写测试 :)< / p >
< h2 id = "dev-dependencies" > < a class = "header" href = "#dev-dependencies" > < code > [dev-dependencies]< / code > < / a > < / h2 >
< p > 与 < code > package.json< / code > ( Nodejs )文件中的 < code > devDependencies< / code > 一样， Rust 也能引入只在开发测试场景使用的外部依赖。< / p >
< p > 其中一个例子就是 < a href = "https://docs.rs/pretty_assertions/1.0.0/pretty_assertions/index.html" > < code > pretty_assertions< / code > < / a > ，它可以用来扩展标准库中的 < code > assert_eq!< / code > 和 < code > assert_ne!< / code > ，例如提供彩色字体的结果对比。< / p >
< p > 在 < code > Cargo.toml< / code > 文件中添加以下内容来引入 < code > pretty_assertions< / code > ： < / p >
< pre > < code class = "language-toml" > # standard crate data is left out
[dev-dependencies]
pretty_assertions = "1"
< / code > < / pre >
< p > 然后在 < code > src/lib.rs< / code > 中添加:< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > pub fn add(a: i32, b: i32) -> i32 {
a + b
}
#[cfg(test)]
mod tests {
use super::*;
use pretty_assertions::assert_eq; // 该包仅能用于测试
#[test]
fn test_add() {
assert_eq!(add(2, 3), 5);
}
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 在 < code > tests< / code > 模块中，我们通过 < code > use pretty_assertions::assert_eq;< / code > 成功的引入之前添加的包，由于 < code > tests< / code > 模块明确的用于测试目的，这种引入并不会报错。 大家可以试试在正常代码(非测试代码)中引入该包，看看会发生什么。< / p >
< h2 id = "生成测试二进制文件" > < a class = "header" href = "#生成测试二进制文件" > 生成测试二进制文件< / a > < / h2 >
< p > 在有些时候，我们可能希望将测试与别人分享，这种情况下生成一个类似 < code > cargo build< / code > 的可执行二进制文件是很好的选择。< / p >
< p > 事实上，在 < code > cargo test< / code > 运行的时候，系统会自动为我们生成一个可运行测试的二进制可执行文件:< / p >
< pre > < code class = "language-shell" > $ cargo test
Finished test [unoptimized + debuginfo] target(s) in 0.00s
Running unittests (target/debug/deps/study_cargo-0d693f72a0f49166)
< / code > < / pre >
< p > 这里的 < code > target/debug/deps/study_cargo-0d693f72a0f49166< / code > 就是可执行文件的路径和名称，我们直接运行该文件来执行编译好的测试:< / p >
< pre > < code class = "language-shell" > $ target/debug/deps/study_cargo-0d693f72a0f49166
running 3 tests
test tests::add_two_and_two ... ok
test tests::add_three_and_two ... ok
test tests::one_hundred ... ok
test result: ok. 3 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
< / code > < / pre >
< p > 如果你只想生成编译生成文件，不想看 < code > cargo test< / code > 的输出结果，还可以使用 < code > cargo test --no-run< / code > .< / p >
< / main >
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