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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"><strong aria-hidden="true">11.2.</strong> Controlling How Tests Are Run</a></li><li class="expanded "><a href="ch11-03-test-organization.html" class="active"><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="#test-organization" id="test-organization">Test Organization</a></h2>
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<p>As mentioned at the start of the chapter, testing is a complex discipline, and
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different people use different terminology and organization. The Rust community
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thinks about tests in terms of two main categories: <em>unit tests</em> and
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<em>integration tests</em>. Unit tests are small and more focused, testing one module
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in isolation at a time, and can test private interfaces. Integration tests are
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entirely external to your library and use your code in the same way any other
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external code would, using only the public interface and potentially exercising
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multiple modules per test.</p>
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<p>Writing both kinds of tests is important to ensure that the pieces of your
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library are doing what you expect them to, separately and together.</p>
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<h3><a class="header" href="#unit-tests" id="unit-tests">Unit Tests</a></h3>
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<p>The purpose of unit tests is to test each unit of code in isolation from the
|
||
rest of the code to quickly pinpoint where code is and isn’t working as
|
||
expected. You’ll put unit tests in the <em>src</em> directory in each file with the
|
||
code that they’re testing. The convention is to create a module named <code>tests</code>
|
||
in each file to contain the test functions and to annotate the module with
|
||
<code>cfg(test)</code>.</p>
|
||
<h4><a class="header" href="#the-tests-module-and-cfgtest" id="the-tests-module-and-cfgtest">The Tests Module and <code>#[cfg(test)]</code></a></h4>
|
||
<p>The <code>#[cfg(test)]</code> annotation on the tests module tells Rust to compile and run
|
||
the test code only when you run <code>cargo test</code>, not when you run <code>cargo build</code>.
|
||
This saves compile time when you only want to build the library and saves space
|
||
in the resulting compiled artifact because the tests are not included. You’ll
|
||
see that because integration tests go in a different directory, they don’t need
|
||
the <code>#[cfg(test)]</code> annotation. However, because unit tests go in the same files
|
||
as the code, you’ll use <code>#[cfg(test)]</code> to specify that they shouldn’t be
|
||
included in the compiled result.</p>
|
||
<p>Recall that when we generated the new <code>adder</code> project in the first section of
|
||
this chapter, Cargo generated this code for us:</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>#[cfg(test)]
|
||
mod tests {
|
||
#[test]
|
||
fn it_works() {
|
||
assert_eq!(2 + 2, 4);
|
||
}
|
||
}
|
||
<span class="boring">}
|
||
</span></code></pre></pre>
|
||
<p>This code is the automatically generated test module. The attribute <code>cfg</code>
|
||
stands for <em>configuration</em> and tells Rust that the following item should only
|
||
be included given a certain configuration option. In this case, the
|
||
configuration option is <code>test</code>, which is provided by Rust for compiling and
|
||
running tests. By using the <code>cfg</code> attribute, Cargo compiles our test code only
|
||
if we actively run the tests with <code>cargo test</code>. This includes any helper
|
||
functions that might be within this module, in addition to the functions
|
||
annotated with <code>#[test]</code>.</p>
|
||
<h4><a class="header" href="#testing-private-functions" id="testing-private-functions">Testing Private Functions</a></h4>
|
||
<p>There’s debate within the testing community about whether or not private
|
||
functions should be tested directly, and other languages make it difficult or
|
||
impossible to test private functions. Regardless of which testing ideology you
|
||
adhere to, Rust’s privacy rules do allow you to test private functions.
|
||
Consider the code in Listing 11-12 with the private function <code>internal_adder</code>.</p>
|
||
<p><span class="filename">Filename: src/lib.rs</span></p>
|
||
<pre><pre class="playpen"><code class="language-rust"><span class="boring">fn main() {}
|
||
</span>
|
||
pub fn add_two(a: i32) -> i32 {
|
||
internal_adder(a, 2)
|
||
}
|
||
|
||
fn internal_adder(a: i32, b: i32) -> i32 {
|
||
a + b
|
||
}
|
||
|
||
#[cfg(test)]
|
||
mod tests {
|
||
use super::*;
|
||
|
||
#[test]
|
||
fn internal() {
|
||
assert_eq!(4, internal_adder(2, 2));
|
||
}
|
||
}
|
||
</code></pre></pre>
|
||
<p><span class="caption">Listing 11-12: Testing a private function</span></p>
|
||
<p>Note that the <code>internal_adder</code> function is not marked as <code>pub</code>, but because
|
||
tests are just Rust code and the <code>tests</code> module is just another module, you can
|
||
bring <code>internal_adder</code> into a test’s scope and call it. If you don’t think
|
||
private functions should be tested, there’s nothing in Rust that will compel
|
||
you to do so.</p>
|
||
<h3><a class="header" href="#integration-tests" id="integration-tests">Integration Tests</a></h3>
|
||
<p>In Rust, integration tests are entirely external to your library. They use your
|
||
library in the same way any other code would, which means they can only call
|
||
functions that are part of your library’s public API. Their purpose is to test
|
||
whether many parts of your library work together correctly. Units of code that
|
||
work correctly on their own could have problems when integrated, so test
|
||
coverage of the integrated code is important as well. To create integration
|
||
tests, you first need a <em>tests</em> directory.</p>
|
||
<h4><a class="header" href="#the-tests-directory" id="the-tests-directory">The <em>tests</em> Directory</a></h4>
|
||
<p>We create a <em>tests</em> directory at the top level of our project directory, next
|
||
to <em>src</em>. Cargo knows to look for integration test files in this directory. We
|
||
can then make as many test files as we want to in this directory, and Cargo
|
||
will compile each of the files as an individual crate.</p>
|
||
<p>Let’s create an integration test. With the code in Listing 11-12 still in the
|
||
<em>src/lib.rs</em> file, make a <em>tests</em> directory, create a new file named
|
||
<em>tests/integration_test.rs</em>, and enter the code in Listing 11-13.</p>
|
||
<p><span class="filename">Filename: tests/integration_test.rs</span></p>
|
||
<pre><code class="language-rust ignore">use adder;
|
||
|
||
#[test]
|
||
fn it_adds_two() {
|
||
assert_eq!(4, adder::add_two(2));
|
||
}
|
||
</code></pre>
|
||
<p><span class="caption">Listing 11-13: An integration test of a function in the
|
||
<code>adder</code> crate</span></p>
|
||
<p>We’ve added <code>use adder</code> at the top of the code, which we didn’t need in the
|
||
unit tests. The reason is that each file in the <code>tests</code> directory is a separate
|
||
crate, so we need to bring our library into each test crate’s scope.</p>
|
||
<p>We don’t need to annotate any code in <em>tests/integration_test.rs</em> with
|
||
<code>#[cfg(test)]</code>. Cargo treats the <code>tests</code> directory specially and compiles files
|
||
in this directory only when we run <code>cargo test</code>. Run <code>cargo test</code> now:</p>
|
||
<pre><code class="language-text">$ cargo test
|
||
Compiling adder v0.1.0 (file:///projects/adder)
|
||
Finished dev [unoptimized + debuginfo] target(s) in 0.31 secs
|
||
Running target/debug/deps/adder-abcabcabc
|
||
|
||
running 1 test
|
||
test tests::internal ... ok
|
||
|
||
test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
|
||
|
||
Running target/debug/deps/integration_test-ce99bcc2479f4607
|
||
|
||
running 1 test
|
||
test it_adds_two ... ok
|
||
|
||
test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
|
||
|
||
Doc-tests adder
|
||
|
||
running 0 tests
|
||
|
||
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
|
||
</code></pre>
|
||
<p>The three sections of output include the unit tests, the integration test, and
|
||
the doc tests. The first section for the unit tests is the same as we’ve been
|
||
seeing: one line for each unit test (one named <code>internal</code> that we added in
|
||
Listing 11-12) and then a summary line for the unit tests.</p>
|
||
<p>The integration tests section starts with the line <code>Running target/debug/deps/integration_test-ce99bcc2479f4607</code> (the hash at the end of
|
||
your output will be different). Next, there is a line for each test function in
|
||
that integration test and a summary line for the results of the integration
|
||
test just before the <code>Doc-tests adder</code> section starts.</p>
|
||
<p>Similarly to how adding more unit test functions adds more result lines to the
|
||
unit tests section, adding more test functions to the integration test file
|
||
adds more result lines to this integration test file’s section. Each
|
||
integration test file has its own section, so if we add more files in the
|
||
<em>tests</em> directory, there will be more integration test sections.</p>
|
||
<p>We can still run a particular integration test function by specifying the test
|
||
function’s name as an argument to <code>cargo test</code>. To run all the tests in a
|
||
particular integration test file, use the <code>--test</code> argument of <code>cargo test</code>
|
||
followed by the name of the file:</p>
|
||
<pre><code class="language-text">$ cargo test --test integration_test
|
||
Finished dev [unoptimized + debuginfo] target(s) in 0.0 secs
|
||
Running target/debug/integration_test-952a27e0126bb565
|
||
|
||
running 1 test
|
||
test it_adds_two ... ok
|
||
|
||
test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
|
||
</code></pre>
|
||
<p>This command runs only the tests in the <em>tests/integration_test.rs</em> file.</p>
|
||
<h4><a class="header" href="#submodules-in-integration-tests" id="submodules-in-integration-tests">Submodules in Integration Tests</a></h4>
|
||
<p>As you add more integration tests, you might want to make more than one file in
|
||
the <em>tests</em> directory to help organize them; for example, you can group the
|
||
test functions by the functionality they’re testing. As mentioned earlier, each
|
||
file in the <em>tests</em> directory is compiled as its own separate crate.</p>
|
||
<p>Treating each integration test file as its own crate is useful to create
|
||
separate scopes that are more like the way end users will be using your crate.
|
||
However, this means files in the <em>tests</em> directory don’t share the same
|
||
behavior as files in <em>src</em> do, as you learned in Chapter 7 regarding how to
|
||
separate code into modules and files.</p>
|
||
<p>The different behavior of files in the <em>tests</em> directory is most noticeable
|
||
when you have a set of helper functions that would be useful in multiple
|
||
integration test files and you try to follow the steps in the <a href="ch07-05-separating-modules-into-different-files.html">“Separating
|
||
Modules into Different Files”</a><!-- ignore -->
|
||
section of Chapter 7 to extract them into a common module. For example, if we
|
||
create <em>tests/common.rs</em> and place a function named <code>setup</code> in it, we can add
|
||
some code to <code>setup</code> that we want to call from multiple test functions in
|
||
multiple test files:</p>
|
||
<p><span class="filename">Filename: tests/common.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 setup() {
|
||
// setup code specific to your library's tests would go here
|
||
}
|
||
<span class="boring">}
|
||
</span></code></pre></pre>
|
||
<p>When we run the tests again, we’ll see a new section in the test output for the
|
||
<em>common.rs</em> file, even though this file doesn’t contain any test functions nor
|
||
did we call the <code>setup</code> function from anywhere:</p>
|
||
<pre><code class="language-text">running 1 test
|
||
test tests::internal ... ok
|
||
|
||
test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
|
||
|
||
Running target/debug/deps/common-b8b07b6f1be2db70
|
||
|
||
running 0 tests
|
||
|
||
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
|
||
|
||
Running target/debug/deps/integration_test-d993c68b431d39df
|
||
|
||
running 1 test
|
||
test it_adds_two ... ok
|
||
|
||
test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
|
||
|
||
Doc-tests adder
|
||
|
||
running 0 tests
|
||
|
||
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
|
||
</code></pre>
|
||
<p>Having <code>common</code> appear in the test results with <code>running 0 tests</code> displayed for
|
||
it is not what we wanted. We just wanted to share some code with the other
|
||
integration test files.</p>
|
||
<p>To avoid having <code>common</code> appear in the test output, instead of creating
|
||
<em>tests/common.rs</em>, we’ll create <em>tests/common/mod.rs</em>. This is an alternate
|
||
naming convention that Rust also understands. Naming the file this way tells
|
||
Rust not to treat the <code>common</code> module as an integration test file. When we move
|
||
the <code>setup</code> function code into <em>tests/common/mod.rs</em> and delete the
|
||
<em>tests/common.rs</em> file, the section in the test output will no longer appear.
|
||
Files in subdirectories of the <em>tests</em> directory don’t get compiled as separate
|
||
crates or have sections in the test output.</p>
|
||
<p>After we’ve created <em>tests/common/mod.rs</em>, we can use it from any of the
|
||
integration test files as a module. Here’s an example of calling the <code>setup</code>
|
||
function from the <code>it_adds_two</code> test in <em>tests/integration_test.rs</em>:</p>
|
||
<p><span class="filename">Filename: tests/integration_test.rs</span></p>
|
||
<pre><code class="language-rust ignore">use adder;
|
||
|
||
mod common;
|
||
|
||
#[test]
|
||
fn it_adds_two() {
|
||
common::setup();
|
||
assert_eq!(4, adder::add_two(2));
|
||
}
|
||
</code></pre>
|
||
<p>Note that the <code>mod common;</code> declaration is the same as the module declaration
|
||
we demonstrated in Listing 7-21. Then in the test function, we can call the
|
||
<code>common::setup()</code> function.</p>
|
||
<h4><a class="header" href="#integration-tests-for-binary-crates" id="integration-tests-for-binary-crates">Integration Tests for Binary Crates</a></h4>
|
||
<p>If our project is a binary crate that only contains a <em>src/main.rs</em> file and
|
||
doesn’t have a <em>src/lib.rs</em> file, we can’t create integration tests in the
|
||
<em>tests</em> directory and bring functions defined in the <em>src/main.rs</em> file into
|
||
scope with a <code>use</code> statement. Only library crates expose functions that other
|
||
crates can use; binary crates are meant to be run on their own.</p>
|
||
<p>This is one of the reasons Rust projects that provide a binary have a
|
||
straightforward <em>src/main.rs</em> file that calls logic that lives in the
|
||
<em>src/lib.rs</em> file. Using that structure, integration tests <em>can</em> test the
|
||
library crate with <code>use</code> to make the important functionality available.
|
||
If the important functionality works, the small amount of code in the
|
||
<em>src/main.rs</em> file will work as well, and that small amount of code doesn’t
|
||
need to be tested.</p>
|
||
<h2><a class="header" href="#summary" id="summary">Summary</a></h2>
|
||
<p>Rust’s testing features provide a way to specify how code should function to
|
||
ensure it continues to work as you expect, even as you make changes. Unit tests
|
||
exercise different parts of a library separately and can test private
|
||
implementation details. Integration tests check that many parts of the library
|
||
work together correctly, and they use the library’s public API to test the code
|
||
in the same way external code will use it. Even though Rust’s type system and
|
||
ownership rules help prevent some kinds of bugs, tests are still important to
|
||
reduce logic bugs having to do with how your code is expected to behave.</p>
|
||
<p>Let’s combine the knowledge you learned in this chapter and in previous
|
||
chapters to work on a project!</p>
|
||
|
||
</main>
|
||
|
||
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