Testing

What the source does

• FilesystemNone observedNo reads or writes in the source
• NetworkNone observedNo outbound calls in the source
• ShellNone observedNo commands run in the source
• DependenciesPinnedNothing floats
• SecretsNone foundNo keys in source

Five audit layers

Gates applied: no behavioural pass.

Audit 0.4.1 · source sha 492f17636999 · 18 Oct 2026Report an issue or request a re-scan

• Publisheroliver-kriska GitHub userOwner of the repository this skill is read from
• Source folderoliver-kriska/claude-elixir-phoenix/plugins/elixir-phoenix/skills/testingThe exact folder we audited
• LicenceMITAs the repository states it
• Commit pinned for this verdict492f17636999A new audit runs when the source changes
• Repository statusNot archivedLast push 2 days ago
• Sandboxed runNot runSkills are read, not executed; layer L4 is skipped

Its description: 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…

---
name: testing
description: "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."
effort: medium
user-invocable: false
paths:
  - "test/**/*_test.exs"
  - "test/support/**/*.ex"
  - "**/*factory*.ex"
---

# 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

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 for speed
- Use `insert()` only when you need DB ID, constraints, or persisted associations

## Quick Patterns

```elixir
# 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

Excerpt, first 3,195 characters of SKILL.md, verbatim from the audited commit. It is text from someone else’s repository, quoted so you can judge it before your agent reads it.

1. 2026-10-18
   ✓SAFE B 89 / 100

   first audit · source 492f17636999

Questions about Testing

• github.com/oliver-kriska/claude-elixir-phoenix/tree/main/plugins — the audited source at commit 492f17636999 and every finding aboveObserved · 18 Oct 2026

Spotted something wrong? Report a correction · Methodology