modify-tests

name	modify-tests
description	Testing patterns for the elixir_cache project. TRIGGER when: writing or modifying tests, test support modules, test configuration, or test helper functions. Also trigger when working with Cache.Sandbox or Cache.SandboxRegistry test patterns. DO NOT TRIGGER when: writing production code that doesn't involve test infrastructure.

Testing Patterns

General Rules

• Run tests with mix test
• Use ErrorMessage structs for error assertions
• Use refute instead of assert !condition
• Use is_nil/1 guard instead of == nil
• Use === and !== for strict comparisons
• Never use Application.put_env in tests — use compile-time config or test-specific function definitions
• When fixing failing tests, first determine whether the code or the test is wrong before choosing what to fix
• Run tests after writing them
• Use async: true where possible

Test Structure

test/
├── test_helper.exs           # Starts Cache.SandboxRegistry, then ExUnit
├── cache_test.exs             # Tests for the main Cache module / use Cache macro
├── cache_sandbox_test.exs     # Tests for Cache.Sandbox and SandboxRegistry
├── cache/
│   ├── agent_test.exs         # Cache.Agent adapter tests
│   ├── con_cache_test.exs     # Cache.ConCache adapter tests
│   ├── dets_test.exs          # Cache.DETS adapter tests
│   ├── ets_test.exs           # Cache.ETS adapter tests
│   ├── redis_test.exs         # Cache.Redis adapter tests
│   └── term_encoder_test.exs  # Cache.TermEncoder tests

Cache Sandbox Testing

The project uses Cache.SandboxRegistry for per-test cache isolation. Setup in test/test_helper.exs:

Cache.SandboxRegistry.start_link()
ExUnit.start()

In test modules, register caches in setup:

setup do
  Cache.SandboxRegistry.start([TestCacheModule])
  :ok
end

This ensures each test process gets isolated cache keys via sandbox ID prefixing.

Compile-Time Environment Branching

Use Mix.env() at compile time (not available at runtime in releases):

if Mix.env() === :test do
  @sandbox true
else
  @sandbox false
end

Test Cache Modules

Tests define inline cache modules with use Cache for testing adapters. Example pattern:

defmodule TestCache do
  use Cache,
    adapter: Cache.ETS,
    name: :test_cache,
    sandbox?: true,
    opts: [type: :set]
end

Testing GenServers and Supervisors

• Start GenServers with start_supervised!/1
• Use {Cache, [TestCache]} in supervision tree for integration tests