Mock accepts what production rejects

What goes wrong

A mock or fake stands in for a real dependency but accepts requests the real one would reject, for example by ignoring the HTTP method or a required header. A change that drops the header passes the test and fails only against the real server.

Example

A mock payment API answers any request on the path, so the test stays green after the Authorization header is accidentally removed, while the real API returns 401.

Not to be confused with

The mock's rules are looser than production's; this is not a mock that never looks at its arguments at all (Argument-Blind Test Double), though the two sit very close.

Discovered by

@sks24git GitHub

Field notes · 6

@sks24git2026-11-05

A screen sent a key the server's whitelist rejects, and every test faked the server with a partial match that ignores extra keys. The approve button failed for two weeks while all checks stayed green.

Assert request bodies with exact equality at a contract edge. Subset matchers let a forbidden key ride along unnoticed.

@sks24git2026-11-04

A race between two requests was tested on an in-memory database that runs queries one at a time. The same ordering wins on every run, so the other interleaving never runs and its bug cannot show up.

Test races on the real database, or force each order by hand. A serial fake always picks one.
Know which guarantees your test double adds. It may hide the bug you test for.

@sks24git2026-11-04

A list endpoint needs a required query parameter, but every mock and sample ignores the query string. The page passes all tests and gets only validation errors from the real server, so the whole tab shows no data.

Make mocks reject what the real side rejects. A mock that takes any query hides a missing parameter.
Check the route signature, not only the response. Samples cover output, not input.

@sks24git2026-10-23

The schema hid two must-have rules inside its annotations, and the tests checked output with a validator that skips them. Every generated file passed the tests and would still fail the receiver's format check.

Run the rules embedded in a schema, not only its types. A validator that skips them passes files the receiver rejects.

@sks24git2026-09-10beat 2 review rounds

An audit row logged the owner the code intended to write, taken from the request. When the compare-and-swap was refused the row kept its old owner, so the trail records a change that never happened.

Audit what the row holds after the write, never what you passed in. A refused swap still writes a confident log line.

@sks24git2026-09-10

A test proved a guard by making a collaborator throw; the real collaborator catches internally and falls back to a seed value. The test passed against behaviour that does not exist.

Read what the real collaborator does before mocking its failure. A mock can prove a path the system cannot take.