Testing

Skill oliver-kriska/claude-elixir-phoenix/targets/codex/skills/testing

Claude Code plugin for Elixir/Phoenix/LiveView — 20 specialist agents, Iron Laws enforcement, and Tidewave MCP integration. Plan features with parallel research agents, execute with automatic verification, review with 4-agent parallel audits, and capture learnings as reusable knowledge.

Install

npx -y skills add oliver-kriska/claude-elixir-phoenix --skill testing

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What its author says it does

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Write or repair Elixir tests with ExUnit, sandbox isolation, async; Use for test files, test setup, or failing/flaky…

SKILL.md

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Elixir Testing Reference

Ash projects: Use DataCase with Ash.Test helpers; test actions via domain code interfaces, not direct Repo calls. See ash-framework skill.

Quick reference for Elixir testing patterns.

Iron Laws — Never Violate These

ASYNC BY DEFAULT — Use async: true unless tests modify global state
SANDBOX ISOLATION — All database tests use Ecto.Adapters.SQL.Sandbox
MOCK ONLY AT BOUNDARIES — Never mock database, internal modules, or stdlib
BEHAVIOURS AS CONTRACTS — All mocks must implement a defined @callback behaviour
BUILD BY DEFAULT — Use build/2 in factories; insert/2 only when DB needed
NO PROCESS.SLEEP — Use assert_receive with timeout for async operations
VERIFY_ON_EXIT! — Always call in Mox tests setup
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 for speed
Use insert() only when you need DB ID, constraints, or persisted associations

Quick Patterns

# Setup chain
setup [:create_user, :authenticate]

# Pattern matching assertion
assert {:ok, %User{name: name}} = create_user(attrs)

# Async message assertion
assert_receive {:user_created, _}, 5000

# Mox setup
setup :verify_on_exit!
expect(MockAPI, :call, fn _ -> {:ok, "data"} end)

# LiveView async
html = render_async(view)  # MUST call for assign_async

Common Anti-patterns

Wrong	Right
`Process.sleep(100)`	`assert_receive {:done, _}, 5000`
`insert(:user)` in factory	`build(:user)` in factory
`async: true` with `set_mox_global()`	`async: false`
Mock internal modules	Test through public API

References

For detailed patterns, see:

references/exunit-patterns.md - Setup, assertions, tags
references/mox-patterns.md - Behaviours, expect/stub, async
references/liveview-testing.md - Forms, async, uploads
references/factory-patterns.md - ExMachina, sequences, traits