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<h1 id="测试驱动开发"><a class="header" href="#测试驱动开发">测试驱动开发</a></h1>
<blockquote>
<p>开始之前，推荐大家先了解下<a href="https://course.rs/test/intro.html">如何在 Rust 中编写测试代码</a>，这块儿内容不复杂，先了解下有利于本章的继续阅读</p>
</blockquote>
<p>在之前的章节中，我们完成了对项目结构的重构，并将进入逻辑代码编程的环节，但在此之前，我们需要先编写一些测试代码，也是最近颇为流行的测试驱动开发模式(TDD, Test Driven Development)：</p>
<ol>
<li>编写一个注定失败的测试，并且失败的原因和你指定的一样</li>
<li>编写一个成功的测试</li>
<li>编写你的逻辑代码，直到通过测试</li>
</ol>
<p>这三个步骤将在我们的开发过程中不断循环，直到所有的代码都开发完成并成功通过所有测试。</p>
<h2 id="注定失败的测试用例"><a class="header" href="#注定失败的测试用例">注定失败的测试用例</a></h2>
<p>既然要添加测试，那之前的 <code>println!</code> 语句将没有大的用处，毕竟 <code>println!</code> 存在的目的就是为了让我们看到结果是否正确，而现在测试用例将取而代之。</p>
<p>接下来，在 <code>lib.rs</code> 文件中，添加 <code>tests</code> 模块和 <code>test</code> 函数: </p>
<pre><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 one_result() {
let query = &quot;duct&quot;;
let contents = &quot;\
Rust:
safe, fast, productive.
Pick three.&quot;;
assert_eq!(vec![&quot;safe, fast, productive.&quot;], search(query, contents));
}
}
<span class="boring">}</span></code></pre></pre>
<p>测试用例将在指定的内容中搜索 <code>duct</code> 字符串，目测可得：其中有一行内容是包含有目标字符串的。</p>
<p>但目前为止，还无法运行该测试用例，更何况还想幸灾乐祸的看其失败，原因是 <code>search</code> 函数还没有实现！毕竟是测试驱动、测试先行。</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>// in lib.rs
pub fn search&lt;'a&gt;(query: &amp;str, contents: &amp;'a str) -&gt; Vec&lt;&amp;'a str&gt; {
vec![]
}
<span class="boring">}</span></code></pre></pre>
<p>先添加一个简单的 <code>search</code> 函数实现，非常简单粗暴的返回一个空的数组，显而易见测试用例将成功通过，真是一个居心叵测的测试用例！</p>
<p>注意这里生命周期 <code>'a</code> 的使用，之前的章节有<a href="https://course.rs/basic/lifetime.html#%E5%87%BD%E6%95%B0%E7%AD%BE%E5%90%8D%E4%B8%AD%E7%9A%84%E7%94%9F%E5%91%BD%E5%91%A8%E6%9C%9F%E6%A0%87%E6%B3%A8">详细介绍</a>，不太明白的同学可以回头看看。</p>
<p>喔，这么复杂的代码，都用上生命周期了！嘚瑟两下试试：</p>
<pre><code class="language-shell">$ cargo test
Compiling minigrep v0.1.0 (file:///projects/minigrep)
Finished test [unoptimized + debuginfo] target(s) in 0.97s
Running unittests src/lib.rs (target/debug/deps/minigrep-9cd200e5fac0fc94)
running 1 test
test tests::one_result ... FAILED
failures:
---- tests::one_result stdout ----
thread 'main' panicked at 'assertion failed: `(left == right)`
left: `[&quot;safe, fast, productive.&quot;]`,
right: `[]`', src/lib.rs:44:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
failures:
tests::one_result
test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
error: test failed, to rerun pass `--lib`
</code></pre>
<p>太棒了！它失败了...</p>
<h2 id="务必成功的测试用例"><a class="header" href="#务必成功的测试用例">务必成功的测试用例</a></h2>
<p>接着就是测试驱动的第二步：编写注定成功的测试。当然，前提条件是实现我们的 <code>search</code> 函数。它包含以下步骤：</p>
<ul>
<li>遍历迭代 <code>contents</code> 的每一行</li>
<li>检查该行内容是否包含我们的目标字符串</li>
<li>若包含，则放入返回值列表中，否则忽略</li>
<li>返回匹配到的返回值列表</li>
</ul>
<h3 id="遍历迭代每一行"><a class="header" href="#遍历迭代每一行">遍历迭代每一行</a></h3>
<p>Rust 提供了一个很便利的 <code>lines</code> 方法将目标字符串进行按行分割:</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>// in lib.rs
pub fn search&lt;'a&gt;(query: &amp;str, contents: &amp;'a str) -&gt; Vec&lt;&amp;'a str&gt; {
for line in contents.lines() {
// do something with line
}
}
<span class="boring">}</span></code></pre></pre>
<p>这里的 <code>lines</code> 返回一个<a href="https://course.rs/advance/functional-programing/iterator.html">迭代器</a>，关于迭代器在后续章节会详细讲解，现在只要知道 <code>for</code> 可以遍历取出迭代器中的值即可。</p>
<h3 id="在每一行中查询目标字符串"><a class="header" href="#在每一行中查询目标字符串">在每一行中查询目标字符串</a></h3>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>// in lib.rs
pub fn search&lt;'a&gt;(query: &amp;str, contents: &amp;'a str) -&gt; Vec&lt;&amp;'a str&gt; {
for line in contents.lines() {
if line.contains(query) {
// do something with line
}
}
}
<span class="boring">}</span></code></pre></pre>
<p>与之前的 <code>lines</code> 函数类似，Rust 的字符串还提供了 <code>contains</code> 方法，用于检查 <code>line</code> 是否包含待查询的 <code>query</code>。</p>
<p>接下来，只要返回合适的值，就可以完成 <code>search</code> 函数的编写。</p>
<h3 id="存储匹配到的结果"><a class="header" href="#存储匹配到的结果">存储匹配到的结果</a></h3>
<p>简单，创建一个 <code>Vec</code> 动态数组，然后将查询到的每一个 <code>line</code> 推进数组中即可：</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>// in lib.rs
pub fn search&lt;'a&gt;(query: &amp;str, contents: &amp;'a str) -&gt; Vec&lt;&amp;'a str&gt; {
let mut results = Vec::new();
for line in contents.lines() {
if line.contains(query) {
results.push(line);
}
}
results
}
<span class="boring">}</span></code></pre></pre>
<p>至此，<code>search</code> 函数已经完成了既定目标，为了检查功能是否正确，运行下我们之前编写的测试用例:</p>
<pre><code class="language-shell">$ cargo test
Compiling minigrep v0.1.0 (file:///projects/minigrep)
Finished test [unoptimized + debuginfo] target(s) in 1.22s
Running unittests src/lib.rs (target/debug/deps/minigrep-9cd200e5fac0fc94)
running 1 test
test tests::one_result ... ok
test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
Running unittests src/main.rs (target/debug/deps/minigrep-9cd200e5fac0fc94)
running 0 tests
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
Doc-tests minigrep
running 0 tests
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
</code></pre>
<p>测试通过，意味着我们的代码也完美运行，接下来就是在 <code>run</code> 函数中大显身手了。</p>
<h3 id="在-run-函数中调用-search-函数"><a class="header" href="#在-run-函数中调用-search-函数">在 run 函数中调用 search 函数</a></h3>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>// in src/lib.rs
pub fn run(config: Config) -&gt; Result&lt;(), Box&lt;dyn Error&gt;&gt; {
let contents = fs::read_to_string(config.file_path)?;
for line in search(&amp;config.query, &amp;contents) {
println!(&quot;{line}&quot;);
}
Ok(())
}
<span class="boring">}</span></code></pre></pre>
<p>好，再运行下看看结果，看起来我们距离成功从未如此之近！</p>
<pre><code class="language-shell">$ cargo run -- frog poem.txt
Compiling minigrep v0.1.0 (file:///projects/minigrep)
Finished dev [unoptimized + debuginfo] target(s) in 0.38s
Running `target/debug/minigrep frog poem.txt`
How public, like a frog
</code></pre>
<p>酷！成功查询到包含 <code>frog</code> 的行，再来试试 <code>body</code> :</p>
<pre><code class="language-shell">$ cargo run -- body poem.txt
Compiling minigrep v0.1.0 (file:///projects/minigrep)
Finished dev [unoptimized + debuginfo] target(s) in 0.0s
Running `target/debug/minigrep body poem.txt`
I'm nobody! Who are you?
Are you nobody, too?
How dreary to be somebody!
</code></pre>
<p>完美，三行，一行不少，为了确保万无一失，再来试试查询一个不存在的单词:</p>
<pre><code class="language-shell">cargo run -- monomorphization poem.txt
Compiling minigrep v0.1.0 (file:///projects/minigrep)
Finished dev [unoptimized + debuginfo] target(s) in 0.0s
Running `target/debug/minigrep monomorphization poem.txt`
</code></pre>
<p>至此，章节开头的目标已经全部完成，接下来思考一个小问题：如果要为程序加上大小写不敏感的控制命令，由用户进行输入，该怎么实现比较好呢？毕竟在实际搜索查询中，同时支持大小写敏感和不敏感还是很重要的。</p>
<p>答案留待下一章节揭晓。</p>
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