rails-testing

name	rails-testing
description	Apply Rails testing standards with Minitest, fixtures, and pragmatic coverage boundaries. Use when creating tests, reviewing test quality, or improving flaky and slow Rails test suites.
disable-model-invocation	true

Rails Testing

Use for test-writing and test-review tasks. Patterns from Campfire and Fizzy test suites.

Defaults

• Minitest + fixtures. No RSpec, no FactoryBot.
• Test behavior, not implementation details.
• Keep tests deterministic and fast; parallelize(workers: :number_of_processors).
• Tests ship in the same commit/PR as the feature — not before, not later. Security fixes always include a regression test.
• Never add production complexity for testability (no test-induced design damage).

Coverage Budget (where 37signals actually spends)

• Heavy: model tests (domain invariants, concerns) and controller/integration tests (full request cycle, auth, formats).
• Light: a few system tests for the critical happy paths (one smoke test can cover signup→use); job tests only for jobs with real logic.
• None: view tests, JS/Stimulus unit tests, exhaustive channel tests. UI behavior is covered indirectly by system tests.
• Don't duplicate the same behavior assertion at multiple layers.

Fixtures

• Express relationships by label, not ID; use ERB for relative timestamps (created_at: <%= 1.hour.ago %>) and shared computed values (one bcrypt digest reused).
• Mirror app/models structure in test/models: app/models/card/closeable.rb ↔ test/models/card/closeable_test.rb; shared concerns under test/models/concerns/.
• UUID PKs break fixture ordering: generate deterministic, label-derived UUIDv7s in fixtures so .first/.last are stable and runtime records are always newer.
• Build rich-content fixtures with production code (ActionText::Attachment.from_attachable(user).to_html), not hand-written markup.

Good Practices

• Use system/integration tests for user workflows; model tests for domain invariants.
• travel_to for time-based logic.
• Mock/stub only at boundaries (external APIs, network, time, SecureRandom); use VCR for external HTTP — auto-name cassettes from class+test name, normalize timestamps in matching.
• Test async side effects from model tests with perform_enqueued_jobs(only: SpecificJob) and assert_enqueued_with — not by unit-testing trivial job classes.
• Correlated count changes in one assertion: assert_difference({ -> { card.assignees.count } => -1, -> { Event.count } => +1 }).
• Test both response formats where controllers serve them: as: :turbo_stream (assert stream targets) and as: :json (status, Location header, body).
• Turbo/broadcast assertions by layer: assert_turbo_stream_broadcasts in model tests, assert_turbo_stream action:, target: in controller tests, assert_no_turbo_stream_broadcasts for negatives.
• Authorization tests assert the negative space: cross-tenant/role access returns 403/404, not just that allowed access works.
• Multi-tenant suites: set Current.account (and Current.session when behavior depends on the actor) in setup; integration/system tests set default_url_options[:script_name]; provide an untenanted { } helper for auth routes. Clear Current in teardown.
• Test middleware in isolation with Rack::MockRequest.
• System tests: using_session("Kevin") for multi-user scenarios; wait for cable connection before asserting realtime; auth via a fast session-transfer helper, keeping the full login flow to one smoke test.
• Suites with non-transactional side effects (FTS tables) opt out per-helper: self.use_transactional_tests = false + explicit cleanup.
• Reset shared global state per test in parallel suites (thread pools, ActionCable.server.pubsub, Current).

Red Flags

• Adding production complexity only for testability.
• Over-mocking internal app code.
• Duplicate tests for the same behavior at multiple layers.
• Slow suites caused by unnecessary setup in each test (that's what fixtures are for).
• Unit tests for one-line job classes or trivial delegations.
• Hand-rolled HTML strings where production renderers/helpers would stay in sync automatically.
• Time-dependent assertions without travel_to.