Mocks and edges

Mocks are use full for simulating objects, we cannot efficiently test locally in unit tests.

Objects that are to test are often objects that proxy access to external systems like Databases or HTTP servers. Using such objects directly in tests will require such external system to be available. At best that will slow down our test. At worst that those systems will maintain state between test, which can influence future tests, making our tests non-deterministic. Even worse those system may share state with other concurrently running test, hurting predictability even further.

This post focuses on how to design for isolation and having confidence when moving from tests to actual integration.

Ground rules

Mocks belong on the edges og your application, if you mock you internal objects, something is broken in the fundamental design.