modify-tests

name	modify-tests
description	Testing patterns for the CheddarFlow project. TRIGGER when: writing or modifying tests, test support modules, test configuration, FactoryEx factories, or test helper functions. Also trigger when setting up HTTP sandboxing, database sandbox, or Oban test helpers. DO NOT TRIGGER when: writing production code that doesn't involve test infrastructure.

Testing Patterns

General Rules

• Always run tests from the app directory: cd apps/my_app && mix test
• Use FactoryEx for all test data — never raw Repo.insert!
• 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

HTTP Sandbox Pattern

API wrapper tests use SharedUtils.Support.HTTPSandbox and SharedUtils.Support.TeslaMock:

defmodule MyApi.SomeTest do
  use SharedUtils.BaseCase, async: true

  alias SharedUtils.Support.TeslaMock

  test "fetches data" do
    TeslaMock.mock([
      {:get, "https://api.example.com/data",
       fn %Tesla.Env{} ->
         %Tesla.Env{status: 200, body: %{"result" => "ok"}}
       end}
    ])

    assert {:ok, _} = MyApi.get_data()
  end
end

Disable sandboxing for integration tests: setup :disable_http_sandbox!

Override adapter: SharedUtils.Support.HTTPSandbox.register_overrides!(adapter: Tesla.Adapter.Httpc)

Database Sandbox

• Schemas.Repo and Schemas.JobsRepo both support Ecto.Adapters.SQL.Sandbox
• SharedUtils.Support.DataCase or equivalent base case modules handle setup

Compile-Time Environment Branching

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

if Mix.env() === :test do
  @default_servers []
else
  @default_servers [%{filter_by: %{side: %{in: [:ask, :above]}}, permanent?: true}]
end

Used for: disabling permanent feed servers in test, adding simulator producers in dev, disabling Oban cleanup, configuring PubSub test topics.

Test Support Modules

• SharedUtils.BaseCase — Base test case with HTTP sandbox
• SharedUtils.Support.TeslaMock — Tesla mock helper
• SharedUtils.Support.HTTPSandbox — HTTP sandboxing via SandboxRegistry
• CFXPubSub.Support.Setup — PubSub test topic configuration
• FactoryEx factories in test/support/ of each app

Testing Oban Workers

use Oban.Testing, repo: Schemas.JobsRepo

test "enqueues job" do
  assert {:ok, _} = MyWorker.new(%{key: "value"}) |> Oban.insert()
  assert_enqueued(worker: MyWorker)
end

Testing GenServers and Supervisors

• Start GenServers with start_supervised!/1
• Feed server test support in shared_feed_utils/test/support/
• PubSub tests: subscribe, trigger event, assert_receive

Property-Based Testing

propcheck available in :test env, primarily in schemas and shared_utils apps.