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<ol class="chapter"><li class="affix"><a href="index.html">Introduction</a></li><li><a href="hello.html"><strong aria-hidden="true">1.</strong> Hello World</a></li><li><ol class="section"><li><a href="hello/comment.html"><strong aria-hidden="true">1.1.</strong> Comments</a></li><li><a href="hello/print.html"><strong aria-hidden="true">1.2.</strong> Formatted print</a></li><li><ol class="section"><li><a href="hello/print/print_debug.html"><strong aria-hidden="true">1.2.1.</strong> Debug</a></li><li><a href="hello/print/print_display.html"><strong aria-hidden="true">1.2.2.</strong> Display</a></li><li><ol class="section"><li><a href="hello/print/print_display/testcase_list.html"><strong aria-hidden="true">1.2.2.1.</strong> Testcase: List</a></li></ol></li><li><a href="hello/print/fmt.html"><strong aria-hidden="true">1.2.3.</strong> Formatting</a></li></ol></li></ol></li><li><a href="primitives.html"><strong aria-hidden="true">2.</strong> Primitives</a></li><li><ol class="section"><li><a href="primitives/literals.html"><strong aria-hidden="true">2.1.</strong> Literals and operators</a></li><li><a href="primitives/tuples.html"><strong aria-hidden="true">2.2.</strong> Tuples</a></li><li><a href="primitives/array.html"><strong aria-hidden="true">2.3.</strong> Arrays and Slices</a></li></ol></li><li><a href="custom_types.html"><strong aria-hidden="true">3.</strong> Custom Types</a></li><li><ol class="section"><li><a href="custom_types/structs.html"><strong aria-hidden="true">3.1.</strong> Structures</a></li><li><a href="custom_types/enum.html"><strong aria-hidden="true">3.2.</strong> Enums</a></li><li><ol class="section"><li><a href="custom_types/enum/enum_use.html"><strong aria-hidden="true">3.2.1.</strong> use</a></li><li><a href="custom_types/enum/c_like.html"><strong aria-hidden="true">3.2.2.</strong> C-like</a></li><li><a href="custom_types/enum/testcase_linked_list.html"><strong aria-hidden="true">3.2.3.</strong> Testcase: linked-list</a></li></ol></li><li><a href="custom_types/constants.html"><strong aria-hidden="true">3.3.</strong> constants</a></li></ol></li><li><a href="variable_bindings.html"><strong aria-hidden="true">4.</strong> Variable Bindings</a></li><li><ol class="section"><li><a href="variable_bindings/mut.html"><strong aria-hidden="true">4.1.</strong> Mutability</a></li><li><a href="variable_bindings/scope.html"><strong aria-hidden="true">4.2.</strong> Scope and Shadowing</a></li><li><a href="variable_bindings/declare.html"><strong aria-hidden="true">4.3.</strong> Declare first</a></li></ol></li><li><a href="types.html"><strong aria-hidden="true">5.</strong> Types</a></li><li><ol class="section"><li><a href="types/cast.html"><strong aria-hidden="true">5.1.</strong> Casting</a></li><li><a href="types/literals.html"><strong aria-hidden="true">5.2.</strong> Literals</a></li><li><a href="types/inference.html"><strong aria-hidden="true">5.3.</strong> Inference</a></li><li><a href="types/alias.html"><strong aria-hidden="true">5.4.</strong> Aliasing</a></li></ol></li><li><a href="conversion.html"><strong aria-hidden="true">6.</strong> Conversion</a></li><li><ol class="section"><li><a href="conversion/from_into.html"><strong aria-hidden="true">6.1.</strong> From and Into</a></li><li><a href="conversion/string.html"><strong aria-hidden="true">6.2.</strong> To and from Strings</a></li></ol></li><li><a href="expression.html"><strong aria-hidden="true">7.</strong> Expressions</a></li><li><a href="flow_control.html"><strong aria-hidden="true">8.</strong> Flow Control</a></li><li><ol class="section"><li><a href="flow_control/if_else.html"><strong aria-hidden="true">8.1.</strong> if/else</a></li><li><a href="flow_control/loop.html"><strong aria-hidden="true">8.2.</strong> loop</a></li><li><ol class="section"><li><a href="flow_control/loop/nested.html"><strong aria-hidden="true">8.2.1.</strong> Nesting and labels</a></li><li><a href="flow_control/loop/return.html"><strong aria-hidden="true">8.2.2.</strong> Returning from loops</a></li></ol></li><li><a href="flow_control/while.html"><strong aria-hidden="true">8.3.</strong> while</a></li><li><a href="flow_control/for.html"><strong aria-hidden="true">8.4.</strong> for and range</a></li><li><a href="flow_control/match.html"><strong aria-hidden="true">8.5.</strong> match</a></li><li><ol class="section"><li><a href="flow_control/match/destructuring.html"><strong aria-hidden="true">8.5.1.</strong> Destructuring</a></li><li><ol class="section"><li><a href="flow_control/match/destructuring/destructure_tuple.html"><strong aria-hidden="true">8.5.1.1.</strong> tuples</a></li><li><a href="flow_control/match/destructuring/destructure_enum.html"><strong aria-hidden="true">8.5.1.2.</strong> enums</a></li><li><a href="flow_control/match/destructuring/destructure_pointers.html"><strong aria-hidden="true">8.5.1.3.</strong> pointers/ref</a></li><li><a href="flow_control/match/destructuring/destructure_structures.html"><strong aria-hidden="true">8.5.1.4.</strong> structs</a></li></ol></li><li><a href="flow_control/match/guard.html"><strong aria-hidden="true">8.5.2.</strong> Guards</a></li><li><a href="flow_control/match/binding.html"><strong aria-hidden="true">8.5.3.</strong> Binding</a></li></ol></li><li><a href="flow_control/if_let.html"><strong aria-hidden="true">8.6.</strong> if let</a></li><li><a href="flow_control/while_let.html"><strong aria-hidden="true">8.7.</strong> while let</a></li></ol></li><li><a href="fn.html"><strong aria-hidden="true">9.</strong> Functions</a></li><li><ol class="section"><li><a href="fn/methods.html"><strong aria-hidden="true">9.1.</strong> Methods</a></li><li><a href="fn/closures.html"><strong aria-hidden="true">9.2.</strong> Closures</a></li><li><ol class="section"><li><a href="fn/closures/capture.html"><strong aria-hidden="true">9.2.1.</strong> Capturing</a></li><li><a href="fn/closures/input_parameters.html"><strong aria-hidden="true">9.2.2.</strong> As input parameters</a></li><li><a href="fn/closures/anonymity.html"><strong aria-hidden="true">9.2.3.</strong> Type anonymity</a></li><li><a href="fn/closures/input_functions.html"><strong aria-hidden="true">9.2.4.</strong> Input functions</a></li><li><a href="fn/closures/output_parameters.html"><strong aria-hidden="true">9.2.5.</strong> As output parameters</a></li><li><a href="fn/closures/closure_examples.html"><strong aria-hidden="true">9.2.6.</strong> Examples in std</a></li><li><ol class="section"><li><a href="fn/closures/closure_examples/iter_any.html"><strong aria-hidden="true">9.2.6.1.</strong> Iterator::any</a></li><li><a href="fn/closures/closure_examples/iter_find.html"><strong aria-hidden="true">9.2.6.2.</strong> Iterator::find</a></li></ol></li></ol></li><li><a href="fn/hof.html"><strong aria-hidden="true">9.3.</strong> Higher Order Functions</a></li><li><a href="fn/diverging.html"><strong aria-hidden="true">9.4.</strong> Diverging functions</a></li></ol></li><li><a href="mod.html"><strong aria-hidden="true">10.</strong> Modules</a></li><li><ol class="section"><li><a href="mod/visibility.html"><strong aria-hidden="true">10.1.</strong> Visibility</a></li><li><a href="mod/struct_visibility.html"><strong aria-hidden="true">10.2.</strong> Struct visibility</a></li><li><a href="mod/use.html"><strong aria-hidden="true">10.3.</strong> The use declaration</a></li><li><a href="mod/super.html"><strong aria-hidden="true">10.4.</strong> super and self</a></li><li><a href="mod/split.html"><strong aria-hidden="true">10.5.</strong> File hierarchy</a></li></ol></li><li><a href="crates.html"><strong aria-hidden="true">11.</strong> Crates</a></li><li><ol class="section"><li><a href="crates/lib.html"><strong aria-hidden="true">11.1.</strong> Library</a></li><li><a href="crates/link.html"><strong aria-hidden="true">11.2.</strong> extern crate</a></li></ol></li><li><a href="cargo.html"><strong aria-hidden="true">12.</strong> Cargo</a></li><li><ol class="section"><li><a href="cargo/deps.html"><strong aria-hidden="true">12.1.</strong> Dependencies</a></li><li><a href="cargo/conventions.html"><strong aria-hidden="true">12.2.</strong> Conventions</a></li><li><a href="cargo/test.html"><strong aria-hidden="true">12.3.</strong> Tests</a></li></ol></li><li><a href="attribute.html"><strong aria-hidden="true">13.</strong> Attributes</a></li><li><ol class="section"><li><a href="attribute/unused.html"><strong aria-hidden="true">13.1.</strong> dead_code</a></li><li><a href="attribute/crate.html"><strong aria-hidden="true">13.2.</strong> Crates</a></li><li><a href="attribute/cfg.html"><strong aria-hidden="true">13.3.</strong> cfg</a></li><li><ol class="section"><li><a href="attribute/cfg/custom.html"><strong aria-hidden="true">13.3.1.</strong> Custom</a></li></ol></li></ol></li><li><a href="generics.html"><strong aria-hidden="true">14.</strong> Generics</a></li><li><ol class="section"><li><a href="generics/gen_fn.html"><strong aria-hidden="true">14.1.</strong> Functions</a></li><li><a href="generics/impl.html"><strong aria-hidden="true">14.2.</strong> Implementation</a></li><li><a href="generics/gen_trait.html"><strong aria-hidden="true">14.3.</strong> Traits</a></li><li><a href="generics/bounds.html"><strong aria-hidden="true">14.4.</strong> Bounds</a></li><li><ol class="section"><li><a href="generics/bounds/testcase_empty.html"><strong aria-hidden="true">14.4.1.</strong> Testcase: empty bounds</a></li></ol></li><li><a href="generics/multi_bounds.html"><strong aria-hidden="true">14.5.</strong> Multiple bounds</a></li><li><a href="generics/where.html"><strong aria-hidden="true">14.6.</strong> Where clauses</a></li><li><a href="generics/new_types.html"><strong aria-hidden="true">14.7.</strong> New Type Idiom</a></li><li><a href="generics/assoc_items.html"><strong aria-hidden="true">14.8.</strong> Associated items</a></li><li><ol class="section"><li><a href="generics/assoc_items/the_problem.html"><strong aria-hidden="true">14.8.1.</strong> The Problem</a></li><li><a href="generics/assoc_items/types.html"><strong aria-hidden="true">14.8.2.</strong> Associated types</a></li></ol></li><li><a href="generics/phantom.html"><strong aria-hidden="true">14.9.</strong> Phantom type parameters</a></li><li><ol class="section"><li><a href="generics/phantom/testcase_units.html"><strong aria-hidden="true">14.9.1.</strong> Testcase: unit clarification</a></li></ol></li></ol></li><li><a href="scope.html"><strong aria-hidden="true">15.</strong> Scoping rules</a></li><li><ol class="section"><li><a href="scope/raii.html"><strong aria-hidden="true">15.1.</strong> RAII</a></li><li><a href="scope/move.html"><strong aria-hidden="true">15.2.</strong> Ownership and moves</a></li><li><ol class="section"><li><a href="scope/move/mut.html"><strong aria-hidden="true">15.2.1.</strong> Mutability</a></li></ol></li><li><a href="scope/borrow.html"><strong aria-hidden="true">15.3.</strong> Borrowing</a></li><li><ol class="section"><li><a href="scope/borrow/mut.html"><strong aria-hidden="true">15.3.1.</strong> Mutability</a></li><li><a href="scope/borrow/freeze.html"><strong aria-hidden="true">15.3.2.</strong> Freezing</a></li><li><a href="scope/borrow/alias.html"><strong aria-hidden="true">15.3.3.</strong> Aliasing</a></li><li><a href="scope/borrow/ref.html"><strong aria-hidden="true">15.3.4.</strong> The ref pattern</a></li></ol></li><li><a href="scope/lifetime.html"><strong aria-hidden="true">15.4.</strong> Lifetimes</a></li><li><ol class="section"><li><a href="scope/lifetime/explicit.html"><strong aria-hidden="true">15.4.1.</strong> Explicit annotation</a></li><li><a href="scope/lifetime/fn.html"><strong aria-hidden="true">15.4.2.</strong> Functions</a></li><li><a href="scope/lifetime/methods.html"><strong aria-hidden="true">15.4.3.</strong> Methods</a></li><li><a href="scope/lifetime/struct.html"><strong aria-hidden="true">15.4.4.</strong> Structs</a></li><li><a href="scope/lifetime/lifetime_bounds.html"><strong aria-hidden="true">15.4.5.</strong> Bounds</a></li><li><a href="scope/lifetime/lifetime_coercion.html"><strong aria-hidden="true">15.4.6.</strong> Coercion</a></li><li><a href="scope/lifetime/static_lifetime.html"><strong aria-hidden="true">15.4.7.</strong> Static</a></li><li><a href="scope/lifetime/elision.html"><strong aria-hidden="true">15.4.8.</strong> Elision</a></li></ol></li></ol></li><li><a href="trait.html"><strong aria-hidden="true">16.</strong> Traits</a></li><li><ol class="section"><li><a href="trait/derive.html"><strong aria-hidden="true">16.1.</strong> Derive</a></li><li><a href="trait/ops.html"><strong aria-hidden="true">16.2.</strong> Operator Overloading</a></li><li><a href="trait/drop.html"><strong aria-hidden="true">16.3.</strong> Drop</a></li><li><a href="trait/iter.html"><strong aria-hidden="true">16.4.</strong> Iterators</a></li><li><a href="trait/clone.html"><strong aria-hidden="true">16.5.</strong> Clone</a></li></ol></li><li><a href="macros.html"><strong aria-hidden="true">17.</strong> macro_rules!</a></li><li><ol class="section"><li><a href="macros/syntax.html"><strong aria-hidden="true">17.1.</strong> Syntax</a></li><li><ol class="section"><li><a href="macros/designators.html"><strong aria-hidden="true">17.1.1.</strong> Designators</a></li><li><a href="macros/overload.html"><strong aria-hidden="true">17.1.2.</strong> Overload</a></li><li><a href="macros/repeat.html"><strong aria-hidden="true">17.1.3.</strong> Repeat</a></li></ol></li><li><a href="macros/dry.html"><strong aria-hidden="true">17.2.</strong> DRY (Don't Repeat Yourself)</a></li><li><a href="macros/dsl.html"><strong aria-hidden="true">17.3.</strong> DSL (Domain Specific Languages)</a></li><li><a href="macros/variadics.html"><strong aria-hidden="true">17.4.</strong> Variadics</a></li></ol></li><li><a href="error.html"><strong aria-hidden="true">18.</strong> Error handling</a></li><li><ol class="section"><li><a href="error/panic.html"><strong aria-hidden="true">18.1.</strong> panic</a></li><li><a href="error/option_unwrap.html"><strong aria-hidden="true">18.2.</strong> Option & unwrap</a></li><li><ol class="section"><li><a href="error/option_unwrap/map.html"><strong aria-hidden="true">18.2.1.</strong> Combinators: map</a></li><li><a href="error/option_unwrap/and_then.html"><strong aria-hidden="true">18.2.2.</strong> Combinators: and_then</a></li></ol></li><li><a href="error/result.html"><strong aria-hidden="true">18.3.</strong> Result</a></li><li><ol class="section"><li><a href="error/result/result_map.html"><strong aria-hidden="true">18.3.1.</strong> map for Result</a></li><li><a href="error/result/result_alias.html"><strong aria-hidden="true">18.3.2.</strong> aliases for Result</a></li><li><a href="error/result/early_returns.html"><strong aria-hidden="true">18.3.3.</strong> Early returns</a></li><li><a href="error/result/enter_question_mark.html"><strong aria-hidden="true">18.3.4.</strong> Introducing ?</a></li></ol></li><li><a href="error/multiple_error_types.html"><strong aria-hidden="true">18.4.</strong> Multiple error types</a></li><li><ol class="section"><li><a href="error/multiple_error_types/option_result.html"><strong aria-hidden="true">18.4.1.</strong> Pulling Results out of Options</a></li><li><a href="error/multiple_error_types/define_error_type.html"><strong aria-hidden="true">18.4.2.</strong> Defining an error type</a></li><li><a href="error/multiple_error_types/boxing_errors.html"><strong aria-hidden="true">18.4.3.</strong> Boxing errors</a></li><li><a href="error/multiple_error_types/reenter_question_mark.html"><strong aria-hidden="true">18.4.4.</strong> Other uses of ?</a></li><li><a href="error/multiple_error_types/wrap_error.html"><strong aria-hidden="true">18.4.5.</strong> Wrapping errors</a></li></ol></li><li><a href="error/iter_result.html"><strong aria-hidden="true">18.5.</strong> Iterating over Results</a></li></ol></li><li><a href="std.html"><strong aria-hidden="true">19.</strong> Std library types</a></li><li><ol class="section"><li><a href="std/box.html"><strong aria-hidden="true">19.1.</strong> Box, stack and heap</a></li><li><a href="std/vec.html"><strong aria-hidden="true">19.2.</strong> Vectors</a></li><li><a href="std/str.html"><strong aria-hidden="true">19.3.</strong> Strings</a></li><li><a href="std/option.html"><strong aria-hidden="true">19.4.</strong> Option</a></li><li><a href="std/result.html"><strong aria-hidden="true">19.5.</strong> Result</a></li><li><ol class="section"><li><a href="std/result/question_mark.html"><strong aria-hidden="true">19.5.1.</strong> ?</a></li></ol></li><li><a href="std/panic.html"><strong aria-hidden="true">19.6.</strong> panic!</a></li><li><a href="std/hash.html"><strong aria-hidden="true">19.7.</strong> HashMap</a></li><li><ol class="section"><li><a 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<a class="header" href="testing/unit_testing.html#unit-testing" id="unit-testing"><h1>Unit testing</h1></a>
<p>Tests are Rust functions that verify that the non-test code is functioning in
the expected manner. The bodies of test functions typically perform some setup,
run the code we want to test, then assert whether the results are what we
expect.</p>
<p>Most unit tests go into a <code>tests</code> <a href="mod.html">mod</a> with the <code>#[cfg(test)]</code> <a href="attribute.html">attribute</a>.
Test functions are marked with the <code>#[test]</code> attribute.</p>
<p>Tests fail when something in the test function <a href="std/panic.html">panics</a>. There are some
helper <a href="macros.html">macros</a>:</p>
<ul>
<li><code>assert!(expression)</code> - panics if expression evaluates to <code>false</code>.</li>
<li><code>assert_eq!(left, right)</code> and <code>assert_ne!(left, right)</code> - testing left and
right expressions for equality and inequality respectively.</li>
</ul>
<pre><code class="language-rust ignore">pub fn add(a: i32, b: i32) -> i32 {
a + b
}
// This is a really bad adding function, its purpose is to fail in this
// example.
#[allow(dead_code)]
fn bad_add(a: i32, b: i32) -> i32 {
a - b
}
#[cfg(test)]
mod tests {
// Note this useful idiom: importing names from outer (for mod tests) scope.
use super::*;
#[test]
fn test_add() {
assert_eq!(add(1, 2), 3);
}
#[test]
fn test_bad_add() {
// This assert would fire and test will fail.
// Please note, that private functions can be tested too!
assert_eq!(bad_add(1, 2), 3);
}
}
</code></pre>
<p>Tests can be run with <code>cargo test</code>.</p>
<pre><code class="language-bash">$ cargo test
running 2 tests
test tests::test_bad_add ... FAILED
test tests::test_add ... ok
failures:
---- tests::test_bad_add stdout ----
thread 'tests::test_bad_add' panicked at 'assertion failed: `(left == right)`
left: `-1`,
right: `3`', src/lib.rs:21:8
note: Run with `RUST_BACKTRACE=1` for a backtrace.
failures:
tests::test_bad_add
test result: FAILED. 1 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out
</code></pre>
<a class="header" href="testing/unit_testing.html#testing-panics" id="testing-panics"><h2>Testing panics</h2></a>
<p>To check functions that should panic under certain circumstances, use attribute
<code>#[should_panic]</code>. This attribute accepts optional parameter <code>expected =</code> with
the text of the panic message. If your function can panic in multiple ways, it helps
make sure your test is testing the correct panic.</p>
<pre><code class="language-rust ignore">pub fn divide_non_zero_result(a: u32, b: u32) -> u32 {
if b == 0 {
panic!("Divide-by-zero error");
} else if a < b {
panic!("Divide result is zero");
}
a / b
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_divide() {
assert_eq!(divide_non_zero_result(10, 2), 5);
}
#[test]
#[should_panic]
fn test_any_panic() {
divide_non_zero_result(1, 0);
}
#[test]
#[should_panic(expected = "Divide result is zero")]
fn test_specific_panic() {
divide_non_zero_result(1, 10);
}
}
</code></pre>
<p>Running these tests gives us:</p>
<pre><code class="language-bash">$ cargo test
running 3 tests
test tests::test_any_panic ... ok
test tests::test_divide ... ok
test tests::test_specific_panic ... ok
test result: ok. 3 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
Doc-tests tmp-test-should-panic
running 0 tests
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
</code></pre>
<a class="header" href="testing/unit_testing.html#running-specific-tests" id="running-specific-tests"><h2>Running specific tests</h2></a>
<p>To run specific tests one may specify the test name to <code>cargo test</code> command.</p>
<pre><code class="language-bash">$ cargo test test_any_panic
running 1 test
test tests::test_any_panic ... ok
test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 2 filtered out
Doc-tests tmp-test-should-panic
running 0 tests
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
</code></pre>
<p>To run multiple tests one may specify part of a test name that matches all the
tests that should be run.</p>
<pre><code class="language-bash">$ cargo test panic
running 2 tests
test tests::test_any_panic ... ok
test tests::test_specific_panic ... ok
test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 1 filtered out
Doc-tests tmp-test-should-panic
running 0 tests
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
</code></pre>
<a class="header" href="testing/unit_testing.html#ignoring-tests" id="ignoring-tests"><h2>Ignoring tests</h2></a>
<p>Tests can be marked with the<code>#[ignore]</code> attribute to exclude some tests. Or to run
them with command <code>cargo test -- --ignored</code></p>
<pre><pre class="playpen"><code class="language-rust">
# #![allow(unused_variables)]
#fn main() {
pub fn add(a: i32, b: i32) -> i32 {
a + b
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_add() {
assert_eq!(add(2, 2), 4);
}
#[test]
fn test_add_hundred() {
assert_eq!(add(100, 2), 102);
assert_eq!(add(2, 100), 102);
}
#[test]
#[ignore]
fn ignored_test() {
assert_eq!(add(0, 0), 0);
}
}
#}</code></pre></pre>
<pre><code class="language-bash">$ cargo test
running 1 test
test tests::ignored_test ... ignored
test result: ok. 0 passed; 0 failed; 1 ignored; 0 measured; 0 filtered out
Doc-tests tmp-ignore
running 0 tests
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
$ cargo test -- --ignored
running 1 test
test tests::ignored_test ... ok
test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
Doc-tests tmp-ignore
running 0 tests
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
</code></pre>
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