Testing

Skill oliver-kriska/claude-elixir-phoenix/plugins/elixir-phoenix/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

Copied from the file, not written here

Write or repair Elixir tests with ExUnit, sandbox isolation, async reliability, Mox, ExMachina, and LiveViewTest. Use for test files, test setup, or failing/flaky tests. NOT for investigating an application bug outside the test suite.

SKILL.md

3.2 KB, as published. Nobody here has run it

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:

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

Gives 0 of the 12 instructions most test skills give

Counted across 964 of the 1,571 authors here whose files we hold, read 2026-08-06

close the browser when donein 55 of 964, across 12 files
wait for network idle statein 51 of 964, across 6 files
launch chromium in headless modein 49 of 964, across 6 files
use descriptive selectors for elementsin 49 of 964, across 6 files
run provided scripts with help flag firstin 49 of 964, across 6 files
add appropriate explicit waitsin 48 of 964, across 5 files
use bundled scripts as black boxesin 46 of 964, across 3 files
do not read script source codein 46 of 964, across 3 files
use sync playwright for scriptsin 46 of 964, across 3 files
inspect dom before executing actionsin 46 of 964, across 3 files
run the full test suitein 36 of 964, across 34 files
write the failing test firstin 25 of 964, across 18 files

Said here and by no other author read

use sandbox isolation for database tests
define behaviours for all mocks
use build in factories by default
use insert only when database is needed
use assert receive with timeout for async operations
call verify on exit in mox test setup

Grouped from the skills themselves: near-identical wordings counted once, and counted by distinct author, so one author publishing three of these counts once.