The alternative to shared examples

Takeaways

• Argues against RSpec shared_examples for mix-ins in favor of isolated contract-tests—spec the mixin module directly, not via including classes.
• Isolated testing: test one file’s contract without re-running lower layers (e.g. don’t hit persistence when speccing a controller).
• Failures map 1:1 to source files; forces explicit thinking about scope, API, and contracts.
• For mix-ins, follow David Chelimsky’s three concerns: at-mix-in-time logic, message-triggered behavior, and how including classes (K, L) assert wellformedness separately.
• Shared examples hide the mixin spec, add setup cost, and blur the link between it blocks and the code under test.

Notes

Part 2 of epigene’s series (pt1: case against shared examples). Practical Ruby/RSpec philosophy applicable beyond Rails—modular specs over DRY-at-all-costs in test suites.

Open questions

• Does this pattern extend cleanly to JS/TS mixin patterns or composition hooks in React?