testing – Page 11 – Türker Yıldırım

The test that failed only when run alone

NoteNovember 21, 20232 min read

The usual failure is a test that passes alone and fails in the suite; this was the reverse, and the reverse is more interesting. A test that depends…

The interface with one implementation, and when that is fine

Deep diveNovember 16, 202310 min read

140 interfaces, 128 of them with exactly one implementation, and a jump-to-definition that always lands on the wrong file.

A snapshot test for an email, and the day it caught something

NoteNovember 13, 20232 min read

Snapshot tests are usually a way of asserting that nothing changed, which is worth very little, until the change is one nobody intended. The snapshot caught a currency…

The unique index we could not add, and the duplicates we had to find first

Deep diveNovember 7, 202310 min read

A constraint that should have existed since 2016, and 1,240 rows that violate it. Support merging customer records by hand, monthly.

Mutation testing on the money code only

NoteOctober 26, 20232 min read

A full mutation run takes nine hours; a run over one directory takes eleven minutes and answers the question that matters. The gap between 94% coverage and 71%…

Mutation testing for one directory, and what it found

Deep diveOctober 24, 202310 min read

94% line coverage on the pricing code, and a bug that shipped anyway. A test that called the method and asserted it did not throw.

A repository interface, one implementation, one fake

NoteSeptember 21, 20232 min read

The argument that an interface with one implementation is waste ignores that the test double is a second implementation, and the argument that the double justifies it ignores…

A value object library, and the day it needed a serializer

Deep diveSeptember 20, 202310 min read

A Money type, an Email type, and thirty more, none of which can cross a boundary without being unwrapped by hand.

An outbox, and the publisher we removed from the transaction

Deep diveSeptember 20, 202310 min read

An order committed and an event never published, twice in one week. A broker call inside a database transaction, and a rollback after it.

Testing a queue by asserting the payload, not the effect

NoteSeptember 20, 20232 min read

A test that dispatched a job and then asserted on the database is testing two things and failing for two reasons. Splitting at the queue boundary is the…