testing

# Elixir Testing Reference Quick reference for Elixir testing patterns. ## Iron Laws — Never Violate These 1. **ASYNC BY DEFAULT** — Use `async: true` unless tests modify global state 2. **SANDBOX ISOLATION** — All database tests use Ecto.Adapters.SQL.Sandbox 3. **MOCK ONLY AT BOUNDARIES** — Never mock database, internal modules, or stdlib 4. **BEHAVIOURS AS CONTRACTS** — All mocks must implement a defined `@callback` behaviour 5. **BUILD BY DEFAULT** — Use `build/2` in factories; `insert/2` only when DB needed 6. **NO PROCESS.SLEEP** — Use `assert_receive` with timeout for async operations 7. **VERIFY_ON_EXIT!** — Always call in Mox tests setup 8. **FACTORIES MATCH SCHEMA REQUIRED FIELDS** — Factory definitions must include all fields that have `validate_required` in the schema changeset. Missing fields cause cascading test failures ## Quick Decisions ### Which Test Case? | Testing | Use | |---------|-----| | Controller/API | `use MyAppWeb.ConnCase` | | Context/Schema | `use MyApp.DataCase` | | LiveView | `use MyAppWeb.ConnCase` + `import Phoenix.LiveViewTest` | | Pure logic | `use ExUnit.Case, async: true` | ### When to use async: true? - ✅ Pure functions, no shared state - ✅ Database tests with Sandbox (PostgreSQL) - ❌ Tests modifying `Application.put_env` - ❌ Tests using Mox global mode ### Mock or not? - ✅ Mock: External APIs, email services, file storage - ❌ Don't mock: Database, internal modules, stdlib ### build() or insert()? - Use `build()` by default fo...