Regression Prevention

Regressions are defects that were previously fixed but reappear. During migration, they can be introduced by transpilation errors, optimization passes, or incorrect type mappings.

Snapshot Testing

Capture known-good output and compare on every test run:

#![allow(unused)]
fn main() {
use insta::assert_snapshot;

#[test]
fn pipeline_report_format() {
    let report = generate_analysis_report("./fixtures/sample_project");
    assert_snapshot!(report);
}
}

Review and accept intentional changes with cargo insta review.

Benchmark Regression Detection

Use Criterion to detect performance regressions:

# Save baseline before migration
cargo bench -- --save-baseline before

# Compare after migration
cargo bench -- --baseline before

Criterion reports statistical significance: +2.3% (p = 0.04) means a real regression.

CI Quality Gates

batuta stack gate

Regression Test Workflow

When a bug is found:

1. Write a failing test that reproduces the bug
2. Fix the bug
3. Tag the test with the issue number

#![allow(unused)]
fn main() {
#[test]
fn regression_cb042_negative_stride() {
    // CB-042: Negative stride caused index overflow
    let result = transpose_with_stride(&data, -1);
    assert!(result.is_ok());
}
}

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