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The content slides all use `fn main`, with the exception of the testing segment. But with this change, where it makes sense exercises use tests instead, and not both tests and `fn main`. A small change in `book.js` supports running tests when a code sample does not have `fn main` but does have `#[test]`, so these work naturally. Fixes #1581.
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Unit Tests
Rust and Cargo come with a simple unit test framework. Tests are marked with
#[test]. Unit tests are often put in a nested tests module, using
#[cfg(test)] to conditionally compile them only when building tests.
fn first_word(text: &str) -> &str {
match text.find(' ') {
Some(idx) => &text[..idx],
None => &text,
}
}
#[cfg(test)]
mod tests {
use super::*;
#[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");
}
}
- This lets you unit test private helpers.
- The
#[cfg(test)]attribute is only active when you runcargo test.