#104 with Rust

How to write and organise tests for rust.

Notes

Rust has first class testing support built into the language and toolchain. It even has a nascent style guide for testing.

Test code is identified with a set of test attributes

#[test] marks a function as a test
#[ignore] disables a test function
#[should_panic] indicates a test is expected to generate a panic
#[cfg(test)] is used to mark a testing module for conditional compilation when running in test mode

The test mode is enabled by passing the --test argument to rustc or using cargo test.

Assertions are supported with a number of macros including:

assert!
assert_eq!
assert_ne!
there are complementary debug_*! forms that are only enabled in non optimized builds by default

Where to put test code:

Unit tests: convention is to create a test module named tests in each file
Integration tests: included in a tests directory at the top level of the project directory, next to src
Doc Tests: executing documentation examples to make sure they still run

Other things to note about testing:

Rust’s privacy rules allow you to test private functions

Testing a Library

$ cargo new tested_lib --lib
     Created library `tested_lib` package
$ cd tested_lib/

Added a few examples/demonstrations to this project including:

unit test module
assertions
expect panic in a test
integration tests
doc tests

Running the tests:

$ cargo test
   Compiling tested_lib v0.1.0 (.../rust/testing/tested_lib)
    Finished test [unoptimized + debuginfo] target(s) in 1.80s
     Running target/debug/deps/tested_lib-bd99122334aecbd7

running 3 tests
test tests::add_private_works ... ok
test tests::add_two_works ... ok
test tests::failing_test ... ok

test result: ok. 3 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

     Running target/debug/deps/integration_test-86734f87d5dcd2ce

running 1 test
test it_adds_two ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

   Doc-tests tested_lib

running 1 test
test src/lib.rs - add_two (line 5) ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

Testing an Application

Integration tests for binary creates face a problem: they can’t use functions from src/main.rs. Solution:

put functionality that needs integration testing in supporting library create so it can be tested
unit test src/main.rs, or just make it so trivial that it doesn’t need additional testing

$ cargo new tested_app
     Created binary (application) `tested_app` package
$ cd tested_app/

$ cargo test
   Compiling tested_app v0.1.0 (.../rust/testing/tested_app)
    Finished test [unoptimized + debuginfo] target(s) in 1.76s
     Running target/debug/deps/tested_app-6874ba1f641ef8b1

running 3 tests
test tests::add_private_works ... ok
test tests::add_two_works ... ok
test tests::failing_test ... ok

test result: ok. 3 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

     Running target/debug/deps/tested_app-893ff5312f83678e

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

     Running target/debug/deps/integration_test-8cd2670c773b8a51

running 1 test
test it_adds_two ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

   Doc-tests tested_app

running 1 test
test src/lib.rs - add_two (line 5) ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

Running the app:

$ cargo run
    Finished dev [unoptimized + debuginfo] target(s) in 0.01s
     Running `target/debug/tested_app`
Adding 2 to 2 = 4

Credits and References

Writing Automated Tests - The Rust Programming Language
Rust basic attributes
Rust test attributes

Project Notes

#104 with Rust

Notes

Testing a Library

Testing an Application

Credits and References