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Elixir Testing Reference · oliver-kriska | DecimalAI

testingby oliver-kriska

Elixir Testing Reference

oliver-kriska/testing

Source oliver-kriska/claude-elixir-phoenix ↗License MIT

Write or repair Elixir tests with ExUnit, sandbox isolation, async reliability, Mox, ExMachina, and LiveViewTest.

NewMaintained

Automatic

QA & Test Engineering pack

Last verified 8/19/2026

What it changes

Passed 11 of 22 test cases with the skill, and 11 of 22 without it.

Without skill50%

With skill50%

Checks it passed that the model alone missed

Recommends using DataCase with Ash.Test helpers for Ash project tests

1 fixed20 passed either way1 still failing0 broke

Pass-rate lift: 0 pp
Tokens: +8%
Agent turns: 0%
Response time: -35%

Model gemini-3.6-flashMeasured 8/19/2026v221 of 22 cases passed with skill

Tokens, turns and time describe resource use, not a dollar price.

Use this skill

Save it into your project's skills folder. Claude Code picks it up in its next session.

curl -fsSL --create-dirs -o .claude/skills/oliver-kriska-testing/SKILL.md https://app.decimal.ai/s/oliver-kriska-testing/SKILL.md

Want it pinned and updatable? pip install "decimalai>=0.15", then decimalai skills add oliver-kriska-testing, and start Claude Code with claude --plugin-dir "$(git rev-parse --show-toplevel)/.agents"

1 · One-time — install the CLI (docs ↗)

pip install "decimalai>=0.15"

2 · Get the skill — writes .agents/skills/oliver-kriska-testing/ and pins it in .decimal/skills.lock

decimalai skills add oliver-kriska-testing

No CLI? Get the same file — curl · raw file

curl -fsSL --create-dirs -o .claude/skills/oliver-kriska-testing/SKILL.md https://app.decimal.ai/s/oliver-kriska-testing/SKILL.md

Raw file: /s/oliver-kriska-testing/SKILL.md ↗ · machine-readable summary at /s/oliver-kriska-testing.json ↗

Safety checks: 3 of 3 passed

Code scan CleanIntent PassedContent Clean

See it in action

A test case the skill fixed. Same model, same prompt, with and without the skill.

Prompt

We are testing an Ash Framework resource in an Elixir application. A team member is writing direct Repo calls inside test helpers to query and assert resource states. What test case and testing approach should be used for Ash projects?

What was checked, without and with the skill
Checked	Without skill	With skill
Recommends using DataCase with Ash.Test helpers for Ash project tests	Missed	Passed
Advises testing actions via domain code interfaces rather than direct Repo calls	Passed	Passed

case-13 · gemini-3.6-flash · 8/19/2026 · answers are capped and redacted

What's inside

The instructions your model reads when the skill loads.

SKILL.md82 lines5 files

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

Track record

Benchmark

11 / 22

test cases passed, vs 11 / 22 without

Adoption

Users: 0
Times used: 0

Safety and source details

SkillSafety

✓ 3 of 3 passed

Code scan15 of 15 checks clean

0 critical · 0 warning · 0 info — scanner v4 — 8/3/2026

View 15 scanner checks

live_secretremote_code_executionreverse_shelldata_exfiltrationssrf_metadataagent_snoopinganti_refusaldestructive_commandsobfuscated_unicodeunicode_homoglyphopaque_blobsuspicious_urltool_overreachtrigger_abuseprompt_injection_phrasing

IntentSafe

LLM judge · does the skill do what it claims

ContentClean

LLM judge · policy & harmful-content review

Source

Imported

oliver-kriska / claude-elixir-phoenix

plugins/elixir-phoenix/skills/testing/SKILL.md

View on GitHub ↗

License MITImported 8/3/2026Version v2Bundled 4 files

More skills from the same source and nearby in the registry, with their headline benchmark lift.

Ready to supercharge your AI agents?

See it in action

What's inside

Elixir Testing Reference

Iron Laws — Never Violate These

Quick Decisions

Which Test Case?

When to use async: true?

Mock or not?

Track record

Benchmark

Adoption

SkillSafety

Source

Related skills