Test Design Desiderata

This skill applies Kent Beck's Test Desiderata framework. The core idea: you cannot maximize every desirable property of a test simultaneously, so make conscious tradeoffs instead of defaulting to "assert everything."

The Tradeoff Mindset

A test that checks every field is not thorough -- it's fragile. A test that mocks every dependency is not isolated -- it's coupled to implementation. More assertions do not mean more confidence; they mean more maintenance.

Before writing any test, ask:

• What behavior would break that a caller would actually notice? Test that.
• If I refactored the internals tomorrow, would this test still pass? If not, you're testing structure, not behavior.
• Does each assertion earn its keep? Every assertion is a maintenance commitment. If it doesn't catch a meaningful regression, remove it.

The 12 Properties

No single test can maximize all of them -- the art is choosing the right tradeoffs.