Testing
Rust and Cargo come with a simple unit test framework:
- Unit tests are supported throughout your code.
- Integration tests are supported via the tests/ directory.
Unit Tests
Mark unit tests with #[test]:
fn first_word(text: &str) -> &str {
match text.find(' ') {
Some(idx) => &text[..idx],
None => &text,
}
}
#[test]
fn test_empty() {
assert_eq!(first_word(""), "");
}
#[test]
fn test_single_word() {
assert_eq!(first_word("Hello"), "Hello");
}
#[test]
fn test_multiple_words() {
assert_eq!(first_word("Hello World"), "Hello");
}Use cargo test to find and run the unit tests.
Test Modules
Unit tests are often put in a nested module
fn helper(a: &str, b: &str) -> String {
format!("{a} {b}")
}
pub fn main() {
println!("{}", helper("Hello", "World"));
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_helper() {
assert_eq!(helper("foo", "bar"), "foo bar");
}
}Hello World- This lets you unit test private helpers.
- The #[cfg(test)] attribute is only active when you run cargo test.
Documentation Tests
Rust has built-in support for documentation tests:
/// Shortens a string to the given length.
///
/// ```
/// use playground::shorten_string;
/// assert_eq!(shorten_string("Hello World", 5), "Hello");
/// assert_eq!(shorten_string("Hello World", 20), "Hello World");
/// ```
pub fn shorten_string(s: &str, length: usize) -> &str {
&s[..std::cmp::min(length, s.len())]
}- Code blocks in / comments are automatically seen as Rust code.
- The code will be compiled and executed as part of cargo test.
Integration Tests
If you want to test your library as a client, use an integration test.
Create a .rs file under tests/:
use my_library::init;
#[test]
fn test_init() {
assert!(init().is_ok());
}These tests only have access to the public API of your crate.
Useful crates for writing tests
Rust comes with only basic support for writing tests.
Here are some additional crates which we recommend for writing tests:
- googletest: Comprehensive test assertion library in the tradition of GoogleTest for C++.
- proptest: Property-based testing for Rust.
- rstest: Support for fixtures and parameterised tests.