tdd-rust

RTK TDD Workflow

Enforce Red-Green-Refactor for all RTK filter development.

The Loop

1. RED   — Write failing test with real fixture
2. GREEN — Implement minimum code to pass
3. REFACTOR — Clean up, verify still passing
4. SAVINGS — Verify ≥60% token reduction
5. SNAPSHOT — Lock output format with insta

Step 1: Real Fixture First

Never write synthetic test data. Capture real command output:

# Capture real output from the actual command
git log -20 > tests/fixtures/git_log_raw.txt
cargo test 2>&1 > tests/fixtures/cargo_test_raw.txt
cargo clippy 2>&1 > tests/fixtures/cargo_clippy_raw.txt
gh pr view 42 > tests/fixtures/gh_pr_view_raw.txt

# For commands with ANSI codes — capture as-is
script -q /dev/null cargo test 2>&1 > tests/fixtures/cargo_test_ansi_raw.txt

Fixture naming: tests/fixtures/<command>_raw.txt

Step 2: Write the Test (Red)

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

    fn count_tokens(s: &str) -> usize {
        s.split_whitespace().count()
    }

    // Test 1: Output format (snapshot)
    #[test]
    fn test_filter_output_format() {
        let input = include_str!("../tests/fixtures/mycmd_raw.txt");
        let output = filter_mycmd(input).expect("filter should not fail");
        assert_snapshot!(output);
    }

    // Test 2: Token savings ≥60%
    #[test]
    fn test_token_savings() {
        let input = include_str!("../tests/fixtures/mycmd_raw.txt");
        let output = filter_mycmd(input).expect("filter should not fail");

        let input_tokens = count_tokens(input);
        let output_tokens = count_tokens(&output);
        let savings = 100.0 * (1.0 - output_tokens as f64 / input_tokens as f64);

        assert!(
            savings >= 60.0,
            "Expected ≥60% token savings, got {:.1}% ({} → {} tokens)",
            savings, input_tokens, output_tokens
        );
    }

    // Test 3: Edge cases
    #[test]
    fn test_empty_input() {
        let result = filter_mycmd("");
        assert!(result.is_ok());
        // Empty input = empty output OR passthrough, never panic
    }

    #[test]
    fn test_malformed_input() {
        let result = filter_mycmd("not valid command output\nrandom text\n");
        // Must not panic — either filter best-effort or return input unchanged
        assert!(result.is_ok());
    }
}