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<ol class="chapter"><li class="expanded affix "><a href="title-page.html">The Rust Programming Language</a></li><li class="expanded affix "><a href="foreword.html">Foreword</a></li><li class="expanded affix "><a href="ch00-00-introduction.html">Introduction</a></li><li class="expanded "><a href="ch01-00-getting-started.html"><strong aria-hidden="true">1.</strong> Getting Started</a></li><li><ol class="section"><li class="expanded "><a href="ch01-01-installation.html"><strong aria-hidden="true">1.1.</strong> Installation</a></li><li class="expanded "><a href="ch01-02-hello-world.html"><strong aria-hidden="true">1.2.</strong> Hello, World!</a></li><li class="expanded "><a href="ch01-03-hello-cargo.html"><strong aria-hidden="true">1.3.</strong> Hello, Cargo!</a></li></ol></li><li class="expanded "><a href="ch02-00-guessing-game-tutorial.html"><strong aria-hidden="true">2.</strong> Programming a Guessing Game</a></li><li class="expanded "><a href="ch03-00-common-programming-concepts.html"><strong aria-hidden="true">3.</strong> Common Programming Concepts</a></li><li><ol class="section"><li class="expanded "><a href="ch03-01-variables-and-mutability.html"><strong aria-hidden="true">3.1.</strong> Variables and Mutability</a></li><li class="expanded "><a href="ch03-02-data-types.html"><strong aria-hidden="true">3.2.</strong> Data Types</a></li><li class="expanded "><a href="ch03-03-how-functions-work.html"><strong aria-hidden="true">3.3.</strong> Functions</a></li><li class="expanded "><a href="ch03-04-comments.html"><strong aria-hidden="true">3.4.</strong> Comments</a></li><li class="expanded "><a href="ch03-05-control-flow.html"><strong aria-hidden="true">3.5.</strong> Control Flow</a></li></ol></li><li class="expanded "><a href="ch04-00-understanding-ownership.html"><strong aria-hidden="true">4.</strong> Understanding Ownership</a></li><li><ol class="section"><li class="expanded "><a href="ch04-01-what-is-ownership.html"><strong aria-hidden="true">4.1.</strong> What is Ownership?</a></li><li class="expanded "><a href="ch04-02-references-and-borrowing.html"><strong aria-hidden="true">4.2.</strong> References and Borrowing</a></li><li class="expanded "><a href="ch04-03-slices.html"><strong aria-hidden="true">4.3.</strong> The Slice Type</a></li></ol></li><li class="expanded "><a href="ch05-00-structs.html"><strong aria-hidden="true">5.</strong> Using Structs to Structure Related Data</a></li><li><ol class="section"><li class="expanded "><a href="ch05-01-defining-structs.html"><strong aria-hidden="true">5.1.</strong> Defining and Instantiating Structs</a></li><li class="expanded "><a href="ch05-02-example-structs.html"><strong aria-hidden="true">5.2.</strong> An Example Program Using Structs</a></li><li class="expanded "><a href="ch05-03-method-syntax.html"><strong aria-hidden="true">5.3.</strong> Method Syntax</a></li></ol></li><li class="expanded "><a href="ch06-00-enums.html"><strong aria-hidden="true">6.</strong> Enums and Pattern Matching</a></li><li><ol class="section"><li class="expanded "><a href="ch06-01-defining-an-enum.html"><strong aria-hidden="true">6.1.</strong> Defining an Enum</a></li><li class="expanded "><a href="ch06-02-match.html"><strong aria-hidden="true">6.2.</strong> The match Control Flow Operator</a></li><li class="expanded "><a href="ch06-03-if-let.html"><strong aria-hidden="true">6.3.</strong> Concise Control Flow with if let</a></li></ol></li><li class="expanded "><a href="ch07-00-managing-growing-projects-with-packages-crates-and-modules.html"><strong aria-hidden="true">7.</strong> Managing Growing Projects with Packages, Crates, and Modules</a></li><li><ol class="section"><li class="expanded "><a href="ch07-01-packages-and-crates.html"><strong aria-hidden="true">7.1.</strong> Packages and Crates</a></li><li class="expanded "><a href="ch07-02-defining-modules-to-control-scope-and-privacy.html"><strong aria-hidden="true">7.2.</strong> Defining Modules to Control Scope and Privacy</a></li><li class="expanded "><a href="ch07-03-paths-for-referring-to-an-item-in-the-module-tree.html"><strong aria-hidden="true">7.3.</strong> Paths for Referring to an Item in the Module Tree</a></li><li class="expanded "><a href="ch07-04-bringing-paths-into-scope-with-the-use-keyword.html"><strong aria-hidden="true">7.4.</strong> Bringing Paths Into Scope with the use Keyword</a></li><li class="expanded "><a href="ch07-05-separating-modules-into-different-files.html"><strong aria-hidden="true">7.5.</strong> Separating Modules into Different Files</a></li></ol></li><li class="expanded "><a href="ch08-00-common-collections.html"><strong aria-hidden="true">8.</strong> Common Collections</a></li><li><ol class="section"><li class="expanded "><a href="ch08-01-vectors.html"><strong aria-hidden="true">8.1.</strong> Storing Lists of Values with Vectors</a></li><li class="expanded "><a href="ch08-02-strings.html"><strong aria-hidden="true">8.2.</strong> Storing UTF-8 Encoded Text with Strings</a></li><li class="expanded "><a href="ch08-03-hash-maps.html"><strong aria-hidden="true">8.3.</strong> Storing Keys with Associated Values in Hash Maps</a></li></ol></li><li class="expanded "><a href="ch09-00-error-handling.html"><strong aria-hidden="true">9.</strong> Error Handling</a></li><li><ol class="section"><li class="expanded "><a href="ch09-01-unrecoverable-errors-with-panic.html"><strong aria-hidden="true">9.1.</strong> Unrecoverable Errors with panic!</a></li><li class="expanded "><a href="ch09-02-recoverable-errors-with-result.html"><strong aria-hidden="true">9.2.</strong> Recoverable Errors with Result</a></li><li class="expanded "><a href="ch09-03-to-panic-or-not-to-panic.html"><strong aria-hidden="true">9.3.</strong> To panic! or Not To panic!</a></li></ol></li><li class="expanded "><a href="ch10-00-generics.html"><strong aria-hidden="true">10.</strong> Generic Types, Traits, and Lifetimes</a></li><li><ol class="section"><li class="expanded "><a href="ch10-01-syntax.html"><strong aria-hidden="true">10.1.</strong> Generic Data Types</a></li><li class="expanded "><a href="ch10-02-traits.html"><strong aria-hidden="true">10.2.</strong> Traits: Defining Shared Behavior</a></li><li class="expanded "><a href="ch10-03-lifetime-syntax.html"><strong aria-hidden="true">10.3.</strong> Validating References with Lifetimes</a></li></ol></li><li class="expanded "><a href="ch11-00-testing.html"><strong aria-hidden="true">11.</strong> Writing Automated Tests</a></li><li><ol class="section"><li class="expanded "><a href="ch11-01-writing-tests.html"><strong aria-hidden="true">11.1.</strong> How to Write Tests</a></li><li class="expanded "><a href="ch11-02-running-tests.html" class="active"><strong aria-hidden="true">11.2.</strong> Controlling How Tests Are Run</a></li><li class="expanded "><a href="ch11-03-test-organization.html"><strong aria-hidden="true">11.3.</strong> Test Organization</a></li></ol></li><li class="expanded "><a href="ch12-00-an-io-project.html"><strong aria-hidden="true">12.</strong> An I/O Project: Building a Command Line Program</a></li><li><ol class="section"><li class="expanded "><a href="ch12-01-accepting-command-line-arguments.html"><strong aria-hidden="true">12.1.</strong> Accepting Command Line Arguments</a></li><li class="expanded "><a href="ch12-02-reading-a-file.html"><strong aria-hidden="true">12.2.</strong> Reading a File</a></li><li class="expanded "><a href="ch12-03-improving-error-handling-and-modularity.html"><strong aria-hidden="true">12.3.</strong> Refactoring to Improve Modularity and Error Handling</a></li><li class="expanded "><a href="ch12-04-testing-the-librarys-functionality.html"><strong aria-hidden="true">12.4.</strong> Developing the Library’s Functionality with Test Driven Development</a></li><li class="expanded "><a href="ch12-05-working-with-environment-variables.html"><strong aria-hidden="true">12.5.</strong> Working with Environment Variables</a></li><li class="expanded "><a href="ch12-06-writing-to-stderr-instead-of-stdout.html"><strong aria-hidden="true">12.6.</strong> Writing Error Messages to Standard Error Instead of Standard Output</a></li></ol></li><li class="expanded "><a href="ch13-00-functional-features.html"><strong aria-hidden="true">13.</strong> Functional Language Features: Iterators and Closures</a></li><li><ol class="section"><li class="expanded "><a href="ch13-01-closures.html"><strong aria-hidden="true">13.1.</strong> Closures: Anonymous Functions that Can Capture Their Environment</a></li><li class="expanded "><a href="ch13-02-iterators.html"><strong aria-hidden="true">13.2.</strong> Processing a Series of Items with Iterators</a></li><li class="expanded "><a href="ch13-03-improving-our-io-project.html"><strong aria-hidden="true">13.3.</strong> Improving Our I/O Project</a></li><li class="expanded "><a href="ch13-04-performance.html"><strong aria-hidden="true">13.4.</strong> Comparing Performance: Loops vs. Iterators</a></li></ol></li><li class="expanded "><a href="ch14-00-more-about-cargo.html"><strong aria-hidden="true">14.</strong> More about Cargo and Crates.io</a></li><li><ol class="section"><li class="expanded "><a href="ch14-01-release-profiles.html"><strong aria-hidden="true">14.1.</strong> Customizing Builds with Release Profiles</a></li><li class="expanded "><a href="ch14-02-publishing-to-crates-io.html"><strong aria-hidden="true">14.2.</strong> Publishing a Crate to Crates.io</a></li><li class="expanded "><a href="ch14-03-cargo-workspaces.html"><strong aria-hidden="true">14.3.</strong> Cargo Workspaces</a></li><li class="expanded "><a href="ch14-04-installing-binaries.html"><strong aria-hidden="true">14.4.</strong> Installing Binaries from Crates.io with cargo install</a></li><li class="expanded "><a href="ch14-05-extending-cargo.html"><strong aria-hidden="true">14.5.</strong> Extending Cargo with Custom Commands</a></li></ol></li><li class="expanded "><a href="ch15-00-smart-pointers.html"><strong aria-hidden="true">15.</strong> Smart Pointers</a></li><li><ol class="section"><li class="expanded "><a href="ch15-01-box.html"><strong aria-hidden="true">15.1.</strong> Using Box<T> to Point to Data on the Heap</a></li><li class="expanded "><a href="ch15-02-deref.html"><strong aria-hidden="true">15.2.</strong> Treating Smart Pointers Like Regular References with the Deref Trait</a></li><li class="expanded "><a href="ch15-03-drop.html"><strong aria-hidden="true">15.3.</strong> Running Code on Cleanup with the Drop Trait</a></li><li class="expanded "><a href="ch15-04-rc.html"><strong aria-hidden="true">15.4.</strong> Rc<T>, the Reference Counted Smart Pointer</a></li><li class="expanded "><a href="ch15-05-interior-mutability.html"><strong aria-hidden="true">15.5.</strong> RefCell<T> and the Interior Mutability Pattern</a></li><li class="expanded "><a href="ch15-06-reference-cycles.html"><strong aria-hidden="true">15.6.</strong> Reference Cycles Can Leak Memory</a></li></ol></li><li class="expanded "><a href="ch16-00-concurrency.html"><strong aria-hidden="true">16.</strong> Fearless Concurrency</a></li><li><ol class="section"><li class="expanded "><a href="ch16-01-threads.html"><strong aria-hidden="true">16.1.</strong> Using Threads to Run Code Simultaneously</a></li><li class="expanded "><a href="ch16-02-message-passing.html"><strong aria-hidden="true">16.2.</strong> Using Message Passing to Transfer Data Between Threads</a></li><li class="expanded "><a href="ch16-03-shared-state.html"><strong aria-hidden="true">16.3.</strong> Shared-State Concurrency</a></li><li class="expanded "><a href="ch16-04-extensible-concurrency-sync-and-send.html"><strong aria-hidden="true">16.4.</strong> Extensible Concurrency with the Sync and Send Traits</a></li></ol></li><li class="expanded "><a href="ch17-00-oop.html"><strong aria-hidden="true">17.</strong> Object Oriented Programming Features of Rust</a></li><li><ol class="section"><li class="expanded "><a href="ch17-01-what-is-oo.html"><strong aria-hidden="true">17.1.</strong> Characteristics of Object-Oriented Languages</a></li><li class="expanded "><a href="ch17-02-trait-objects.html"><strong aria-hidden="true">17.2.</strong> Using Trait Objects That Allow for Values of Different Types</a></li><li class="expanded "><a href="ch17-03-oo-design-patterns.html"><strong aria-hidden="true">17.3.</strong> Implementing an Object-Oriented Design Pattern</a></li></ol></li><li class="expanded "><a href="ch18-00-patterns.html"><strong aria-hidden="true">18.</strong> Patterns and Matching</a></li><li><ol class="section"><li class="expanded "><a href="ch18-01-all-the-places-for-patterns.html"><strong aria-hidden="true">18.1.</strong> All the Places Patterns Can Be Used</a></li><li class="expanded "><a href="ch18-02-refutability.html"><strong aria-hidden="true">18.2.</strong> Refutability: Whether a Pattern Might Fail to Match</a></li><li class="expanded "><a href="ch18-03-pattern-syntax.html"><strong aria-hidden="true">18.3.</strong> Pattern Syntax</a></li></ol></li><li class="expanded "><a href="ch19-00-advanced-features.html"><strong aria-hidden="true">19.</strong> Advanced Features</a></li><li><ol class="section"><li class="expanded "><a href="ch19-01-unsafe-rust.html"><strong aria-hidden="true">19.1.</strong> Unsafe Rust</a></li><li class="expanded "><a href="ch19-03-advanced-traits.html"><strong aria-hidden="true">19.2.</strong> Advanced Traits</a></li><li class="expanded "><a href="ch19-04-advanced-types.html"><strong aria-hidden="true">19.3.</strong> Advanced Types</a></li><li class="expanded "><a href="ch19-05-advanced-functions-and-closures.html"><strong aria-hidden="true">19.4.</strong> Advanced Functions and Closures</a></li><li class="expanded "><a href="ch19-06-macros.html"><strong aria-hidden="true">19.5.</strong> Macros</a></li></ol></li><li class="expanded "><a href="ch20-00-final-project-a-web-server.html"><strong aria-hidden="true">20.</strong> Final Project: Building a Multithreaded Web Server</a></li><li><ol class="section"><li class="expanded "><a href="ch20-01-single-threaded.html"><strong aria-hidden="true">20.1.</strong> Building a Single-Threaded Web Server</a></li><li class="expanded "><a href="ch20-02-multithreaded.html"><strong aria-hidden="true">20.2.</strong> Turning Our Single-Threaded Server into a Multithreaded Server</a></li><li class="expanded "><a href="ch20-03-graceful-shutdown-and-cleanup.html"><strong aria-hidden="true">20.3.</strong> Graceful Shutdown and Cleanup</a></li></ol></li><li class="expanded "><a href="appendix-00.html"><strong aria-hidden="true">21.</strong> Appendix</a></li><li><ol class="section"><li class="expanded "><a href="appendix-01-keywords.html"><strong aria-hidden="true">21.1.</strong> A - Keywords</a></li><li class="expanded "><a href="appendix-02-operators.html"><strong aria-hidden="true">21.2.</strong> B - Operators and Symbols</a></li><li class="expanded "><a href="appendix-03-derivable-traits.html"><strong aria-hidden="true">21.3.</strong> C - Derivable Traits</a></li><li class="expanded "><a href="appendix-04-useful-development-tools.html"><strong aria-hidden="true">21.4.</strong> D - Useful Development Tools</a></li><li class="expanded "><a href="appendix-05-editions.html"><strong aria-hidden="true">21.5.</strong> E - Editions</a></li><li class="expanded "><a href="appendix-06-translation.html"><strong aria-hidden="true">21.6.</strong> F - Translations of the Book</a></li><li class="expanded "><a href="appendix-07-nightly-rust.html"><strong aria-hidden="true">21.7.</strong> G - How Rust is Made and “Nightly Rust”</a></li></ol></li></ol>
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<h2><a class="header" href="#controlling-how-tests-are-run" id="controlling-how-tests-are-run">Controlling How Tests Are Run</a></h2>
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<p>Just as <code>cargo run</code> compiles your code and then runs the resulting binary,
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<code>cargo test</code> compiles your code in test mode and runs the resulting test
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binary. You can specify command line options to change the default behavior of
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<code>cargo test</code> is to run all the tests in parallel and capture output generated
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<p>Some command line options go to <code>cargo test</code>, and some go to the resulting test
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binary. To separate these two types of arguments, you list the arguments that
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go to <code>cargo test</code> followed by the separator <code>--</code> and then the ones that go to
|
||
the test binary. Running <code>cargo test --help</code> displays the options you can use
|
||
with <code>cargo test</code>, and running <code>cargo test -- --help</code> displays the options you
|
||
can use after the separator <code>--</code>.</p>
|
||
<h3><a class="header" href="#running-tests-in-parallel-or-consecutively" id="running-tests-in-parallel-or-consecutively">Running Tests in Parallel or Consecutively</a></h3>
|
||
<p>When you run multiple tests, by default they run in parallel using threads.
|
||
This means the tests will finish running faster so you can get feedback quicker
|
||
on whether or not your code is working. Because the tests are running at the
|
||
same time, make sure your tests don’t depend on each other or on any shared
|
||
state, including a shared environment, such as the current working directory or
|
||
environment variables.</p>
|
||
<p>For example, say each of your tests runs some code that creates a file on disk
|
||
named <em>test-output.txt</em> and writes some data to that file. Then each test reads
|
||
the data in that file and asserts that the file contains a particular value,
|
||
which is different in each test. Because the tests run at the same time, one
|
||
test might overwrite the file between when another test writes and reads the
|
||
file. The second test will then fail, not because the code is incorrect but
|
||
because the tests have interfered with each other while running in parallel.
|
||
One solution is to make sure each test writes to a different file; another
|
||
solution is to run the tests one at a time.</p>
|
||
<p>If you don’t want to run the tests in parallel or if you want more fine-grained
|
||
control over the number of threads used, you can send the <code>--test-threads</code> flag
|
||
and the number of threads you want to use to the test binary. Take a look at
|
||
the following example:</p>
|
||
<pre><code class="language-text">$ cargo test -- --test-threads=1
|
||
</code></pre>
|
||
<p>We set the number of test threads to <code>1</code>, telling the program not to use any
|
||
parallelism. Running the tests using one thread will take longer than running
|
||
them in parallel, but the tests won’t interfere with each other if they share
|
||
state.</p>
|
||
<h3><a class="header" href="#showing-function-output" id="showing-function-output">Showing Function Output</a></h3>
|
||
<p>By default, if a test passes, Rust’s test library captures anything printed to
|
||
standard output. For example, if we call <code>println!</code> in a test and the test
|
||
passes, we won’t see the <code>println!</code> output in the terminal; we’ll see only the
|
||
line that indicates the test passed. If a test fails, we’ll see whatever was
|
||
printed to standard output with the rest of the failure message.</p>
|
||
<p>As an example, Listing 11-10 has a silly function that prints the value of its
|
||
parameter and returns 10, as well as a test that passes and a test that fails.</p>
|
||
<p><span class="filename">Filename: src/lib.rs</span></p>
|
||
<pre><pre class="playpen"><code class="language-rust panics">
|
||
<span class="boring">#![allow(unused_variables)]
|
||
</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></pre>
|
||
<p><span class="caption">Listing 11-10: Tests for a function that calls
|
||
<code>println!</code></span></p>
|
||
<p>When we run these tests with <code>cargo test</code>, we’ll see the following output:</p>
|
||
<pre><code class="language-text">running 2 tests
|
||
test tests::this_test_will_pass ... ok
|
||
test tests::this_test_will_fail ... FAILED
|
||
|
||
failures:
|
||
|
||
---- tests::this_test_will_fail stdout ----
|
||
I got the value 8
|
||
thread 'tests::this_test_will_fail' panicked at 'assertion failed: `(left == right)`
|
||
left: `5`,
|
||
right: `10`', src/lib.rs:19:9
|
||
note: Run with `RUST_BACKTRACE=1` for a backtrace.
|
||
|
||
failures:
|
||
tests::this_test_will_fail
|
||
|
||
test result: FAILED. 1 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out
|
||
</code></pre>
|
||
<p>Note that nowhere in this output do we see <code>I got the value 4</code>, which is what
|
||
is printed when the test that passes runs. That output has been captured. The
|
||
output from the test that failed, <code>I got the value 8</code>, appears in the section
|
||
of the test summary output, which also shows the cause of the test failure.</p>
|
||
<p>If we want to see printed values for passing tests as well, we can disable the
|
||
output capture behavior by using the <code>--nocapture</code> flag:</p>
|
||
<pre><code class="language-text">$ cargo test -- --nocapture
|
||
</code></pre>
|
||
<p>When we run the tests in Listing 11-10 again with the <code>--nocapture</code> flag, we
|
||
see the following output:</p>
|
||
<pre><code class="language-text">running 2 tests
|
||
I got the value 4
|
||
I got the value 8
|
||
test tests::this_test_will_pass ... ok
|
||
thread 'tests::this_test_will_fail' panicked at 'assertion failed: `(left == right)`
|
||
left: `5`,
|
||
right: `10`', src/lib.rs:19:9
|
||
note: Run with `RUST_BACKTRACE=1` for a backtrace.
|
||
test tests::this_test_will_fail ... FAILED
|
||
|
||
failures:
|
||
|
||
failures:
|
||
tests::this_test_will_fail
|
||
|
||
test result: FAILED. 1 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out
|
||
</code></pre>
|
||
<p>Note that the output for the tests and the test results are interleaved; the
|
||
reason is that the tests are running in parallel, as we talked about in the
|
||
previous section. Try using the <code>--test-threads=1</code> option and the <code>--nocapture</code>
|
||
flag, and see what the output looks like then!</p>
|
||
<h3><a class="header" href="#running-a-subset-of-tests-by-name" id="running-a-subset-of-tests-by-name">Running a Subset of Tests by Name</a></h3>
|
||
<p>Sometimes, running a full test suite can take a long time. If you’re working on
|
||
code in a particular area, you might want to run only the tests pertaining to
|
||
that code. You can choose which tests to run by passing <code>cargo test</code> the name
|
||
or names of the test(s) you want to run as an argument.</p>
|
||
<p>To demonstrate how to run a subset of tests, we’ll create three tests for our
|
||
<code>add_two</code> function, as shown in Listing 11-11, and choose which ones to run.</p>
|
||
<p><span class="filename">Filename: src/lib.rs</span></p>
|
||
<pre><pre class="playpen"><code class="language-rust">
|
||
<span class="boring">#![allow(unused_variables)]
|
||
</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></pre>
|
||
<p><span class="caption">Listing 11-11: Three tests with three different
|
||
names</span></p>
|
||
<p>If we run the tests without passing any arguments, as we saw earlier, all the
|
||
tests will run in parallel:</p>
|
||
<pre><code class="language-text">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
|
||
</code></pre>
|
||
<h4><a class="header" href="#running-single-tests" id="running-single-tests">Running Single Tests</a></h4>
|
||
<p>We can pass the name of any test function to <code>cargo test</code> to run only that test:</p>
|
||
<pre><code class="language-text">$ cargo test one_hundred
|
||
Finished dev [unoptimized + debuginfo] target(s) in 0.0 secs
|
||
Running target/debug/deps/adder-06a75b4a1f2515e9
|
||
|
||
running 1 test
|
||
test tests::one_hundred ... ok
|
||
|
||
test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 2 filtered out
|
||
</code></pre>
|
||
<p>Only the test with the name <code>one_hundred</code> ran; the other two tests didn’t match
|
||
that name. The test output lets us know we had more tests than what this
|
||
command ran by displaying <code>2 filtered out</code> at the end of the summary line.</p>
|
||
<p>We can’t specify the names of multiple tests in this way; only the first value
|
||
given to <code>cargo test</code> will be used. But there is a way to run multiple tests.</p>
|
||
<h4><a class="header" href="#filtering-to-run-multiple-tests" id="filtering-to-run-multiple-tests">Filtering to Run Multiple Tests</a></h4>
|
||
<p>We can specify part of a test name, and any test whose name matches that value
|
||
will be run. For example, because two of our tests’ names contain <code>add</code>, we can
|
||
run those two by running <code>cargo test add</code>:</p>
|
||
<pre><code class="language-text">$ cargo test add
|
||
Finished dev [unoptimized + debuginfo] target(s) in 0.0 secs
|
||
Running target/debug/deps/adder-06a75b4a1f2515e9
|
||
|
||
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
|
||
</code></pre>
|
||
<p>This command ran all tests with <code>add</code> in the name and filtered out the test
|
||
named <code>one_hundred</code>. Also note that the module in which a test appears becomes
|
||
part of the test’s name, so we can run all the tests in a module by filtering
|
||
on the module’s name.</p>
|
||
<h3><a class="header" href="#ignoring-some-tests-unless-specifically-requested" id="ignoring-some-tests-unless-specifically-requested">Ignoring Some Tests Unless Specifically Requested</a></h3>
|
||
<p>Sometimes a few specific tests can be very time-consuming to execute, so you
|
||
might want to exclude them during most runs of <code>cargo test</code>. Rather than
|
||
listing as arguments all tests you do want to run, you can instead annotate the
|
||
time-consuming tests using the <code>ignore</code> attribute to exclude them, as shown
|
||
here:</p>
|
||
<p><span class="filename">Filename: src/lib.rs</span></p>
|
||
<pre><pre class="playpen"><code class="language-rust">
|
||
<span class="boring">#![allow(unused_variables)]
|
||
</span><span class="boring">fn main() {
|
||
</span>#[test]
|
||
fn it_works() {
|
||
assert_eq!(2 + 2, 4);
|
||
}
|
||
|
||
#[test]
|
||
#[ignore]
|
||
fn expensive_test() {
|
||
// code that takes an hour to run
|
||
}
|
||
<span class="boring">}
|
||
</span></code></pre></pre>
|
||
<p>After <code>#[test]</code> we add the <code>#[ignore]</code> line to the test we want to exclude. Now
|
||
when we run our tests, <code>it_works</code> runs, but <code>expensive_test</code> doesn’t:</p>
|
||
<pre><code class="language-text">$ cargo test
|
||
Compiling adder v0.1.0 (file:///projects/adder)
|
||
Finished dev [unoptimized + debuginfo] target(s) in 0.24 secs
|
||
Running target/debug/deps/adder-ce99bcc2479f4607
|
||
|
||
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
|
||
</code></pre>
|
||
<p>The <code>expensive_test</code> function is listed as <code>ignored</code>. If we want to run only
|
||
the ignored tests, we can use <code>cargo test -- --ignored</code>:</p>
|
||
<pre><code class="language-text">$ cargo test -- --ignored
|
||
Finished dev [unoptimized + debuginfo] target(s) in 0.0 secs
|
||
Running target/debug/deps/adder-ce99bcc2479f4607
|
||
|
||
running 1 test
|
||
test expensive_test ... ok
|
||
|
||
test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 1 filtered out
|
||
</code></pre>
|
||
<p>By controlling which tests run, you can make sure your <code>cargo test</code> results
|
||
will be fast. When you’re at a point where it makes sense to check the results
|
||
of the <code>ignored</code> tests and you have time to wait for the results, you can run
|
||
<code>cargo test -- --ignored</code> instead.</p>
|
||
|
||
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|
||
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