By the end of this lesson
Verify the downloaded program, inspect its limits and choose a next practice task.
Before you start
- Rust 1.90.0 or later, a terminal and a plain-text editor. Examples were tested with Rust 1.90.0, Edition 2024 on Linux.
- Complete lesson 29, or be comfortable explaining and running its examples.
Three words to know
- Regression test
- A recorded case that protects behaviour when code changes.
- stderr/stdout separation
- Diagnostics and reports use different streams.
- Review scope
- What was actually tested, and what remains outside the evidence.
1. Understand the idea
The downloadable source includes sixteen test functions for the parser and formatter. They cover valid counts, optional final LF, duplicate rows, invalid status/header/title/UTF-8, BOM and CRLF rejection, blank records and byte/row boundaries. A project-level run should also check the CLI boundary: missing paths, extra arguments and late invalid rows must not produce a partial report. Test names describe intent, not a certification of production readiness.
2. Save, run and observe
Save this complete program as status_test.rs in a fresh practice folder. It replaces that lesson file only; keep earlier examples separately. Compile it with rustc, then run the executable. Rust source goes in the editor; rustc and cargo commands go in the terminal.
cargo test --offlineWhat you should see · example output
The built-in tests report 16 passed and 0 failed; timing and harness formatting vary.
fn accepts_status(value: &str) -> bool { matches!(value, "open" | "closed") }
fn main() { println!("uppercase={}", accepts_status("OPEN")); }
#[cfg(test)]
mod tests {
use super::*;
#[test] fn accepts_known() { assert!(accepts_status("open")); assert!(accepts_status("closed")); }
#[test] fn rejects_other() { assert!(!accepts_status("OPEN")); assert!(!accepts_status("")); }
}
What you should see · example output
uppercase=false
3. Explain the result
This route covers foundations, not the whole Rust language. Async runtimes, threads, advanced smart pointers, unsafe Rust, FFI, web frameworks, distributed services and production deployment need separate study. Choose a published Rust recipe and read its inputs, version, licence and recorded test scope before adapting it. No recipe is executed by reading or copying this lesson. For the next exercise, explain the project without looking at the code, then add a failing boundary test before changing behaviour.
YOUR TURN
A small check before you continue
An input has a valid first record and an invalid second status. What should the CLI emit?
Show a suggested answer
No stdout report, error: invalid input on stderr and exit status 2. A total for the first row would be a misleading partial result.
Sources and scope
Documentation and examples reviewed 2026-10-18. Provider screens, package versions and output wording can differ. Examples show expected outcomes; they are not a claim that OpenViST connected to your server or verified your setup.