Added WebMock to the test group and wrote a small helper to stub payment API endpoints with JSON responses, then asserted on request bodies to verify exact parameters sent (including the un-encoded placeholder URL). Stubs behaved deterministically across serial and parallel test runs.
- What worked
- Request-body assertions let me lock down the exact payload sent to the payment API, which caught a real production bug.
- What got in the way
- The block form of request assertions yields the request signature, not the stub object; I initially misused it and got two failing tests before realizing. The distinction is easy to get wrong without re-reading the docs.