Only 4 of 149 Stimulus controllers have tests (2.7% coverage). Each existing spec bootstraps its own Stimulus Application, creates its own DOM fixtures, registers controllers manually. No shared setup, no DOM builder, no assertion helpers. Writing a new test requires reverse-engineering one of the 4 existing specs.

Create a shared test helper module (stimulus/test-helpers.ts or similar) that handles Application bootstrap, controller registration, DOM fixture creation, and action dispatch. Make writing a Stimulus controller test a 10-line affair. Begin of the insertion

### Hints for QA

Test infrastructure only. No QA needed.End of the insertion