tdd-rust

TDD Workflow for Rust Projects

Enforce strict Test-Driven Development: Red → Green → Refactor

Workflow Steps

1. RED: Write failing test first

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_parse_session_metadata() {
        let path = Path::new("tests/fixtures/session.jsonl");
        let metadata = extract_metadata(path).unwrap();

        assert_eq!(metadata.message_count, 42);
        assert!(metadata.first_timestamp < metadata.last_timestamp);
    }
}

Run test to verify failure:

cargo test test_parse_session_metadata
# Expected: FAILED (function doesn't exist yet)

2. GREEN: Implement minimal code to pass

pub fn extract_metadata(path: &Path) -> anyhow::Result<SessionMetadata> {
    // Minimal implementation
    Ok(SessionMetadata {
        message_count: 42, // Hardcoded for first pass
        first_timestamp: Utc::now(),
        last_timestamp: Utc::now(),
        // ...
    })
}

Run test again:

cargo test test_parse_session_metadata
# Expected: PASSED

3. REFACTOR: Improve implementation

pub fn extract_metadata(path: &Path) -> anyhow::Result<SessionMetadata> {
    let file = File::open(path).context("Failed to open session file")?;
    let reader = BufReader::new(file);

    let mut first_line: Option<SessionLine> = None;
    let mut last_line: Option<SessionLine> = None;
    let mut count = 0;

    for line in reader.lines() {
        let line = line?;
        if let Ok(parsed) = serde_json::from_str::<SessionLine>(&line) {
            if first_line.is_none() {
                first_line = Some(parsed.clone());
            }
            last_line = Some(parsed);
            count += 1;
        }
    }

    Ok(SessionMetadata {
        message_count: count,
        first_timestamp: first_line.map(|l| l.timestamp).unwrap_or_else(Utc::now),
        last_timestamp: last_line.map(|l| l.timestamp).unwrap_or_else(Utc::now),
        // ...
    })
}

Final verification:

cargo test test_parse_session_metadata
cargo clippy --all-targets