Testing Shared (all languages) active any

Existing compatibility tests are preserved when public behavior changes

test-002

Intent

When public behavior changes, teams should add new compatibility evidence instead of weakening or deleting the old evidence that protects existing consumers.

Applicability

Applies when a diff changes a published API, service contract, or other consumer-visible behavior and also changes existing compatibility or contract tests. Return unknown when the repository has no visible compatibility tests for that surface.

What to inspect

Check deleted or weakened assertions, changed compatibility suites, CDC artifacts if the repo uses them, and whether prior behavior is still exercised alongside the new behavior.

Pass criteria

Existing compatibility coverage for preserved behavior stays in place, and new behavior is covered with additional tests instead of by weakening the prior suite.

Fail criteria

The diff removes, disables, or materially weakens existing compatibility evidence for still-supported behavior without an equivalent replacement.

Do not flag

Pure test refactors that preserve meaning, movement of tests between files with equivalent assertions, or retirement of a clearly removed version whose shutdown path is separately covered.

Confidence guidance

HIGH when assertions are deleted or loosened in the same PR as the public behavior change. MEDIUM when helper or generated test structure obscures equivalence. LOW when the source of truth lives elsewhere.

Remediation

Keep the old compatibility assertions and add separate tests for the new or changed behavior.

Pass example

describe('v1 compatibility', () => {
  it('still accepts requests without postalCode', async () => {
    const res = await request(app).post('/users').send({ email: 'a@example.com' });
    expect(res.status).toBe(201);
  });
});

Fail example

// Old compatibility assertion deleted and replaced with only the new path.
it('creates user', async () => {
  const res = await request(app).post('/users').send({ email: 'a@example.com', postalCode: '12345' });
  expect(res.status).toBe(201);
});