Inertia Rails Testing

Testing patterns for Inertia responses with RSpec and Minitest.

For each controller action, verify:

• Correct component → render_component('users/index')
• Expected props → have_props(users: satisfy { ... })
• No leaked data → havenoprop(:secret)
• Flash messages → followredirect! then haveflash(notice: '...')
• Deferred props → havedeferredprops(:analytics)

Common mistake: Forgetting follow_redirect! after PRG — without it, you're asserting against the 302 redirect response, not the Inertia page that follows.

Setup

# spec/rails_helper.rb
require 'inertia_rails/rspec'

RSpec Matchers

RSpec Examples

ALWAYS use matchers (rendercomponent, haveprops, have_flash) instead of direct property access (inertia.component, inertia.props[:key]):

# BAD — direct property access:
# expect(inertia.component).to eq('users/index')
# expect(inertia.props[:users].length).to eq(3)

# GOOD — use matchers:
expect(inertia).to render_component('users/index')
expect(inertia).to have_props(users: satisfy { |u| u.length == 3 })

# Key pattern: follow_redirect! after POST/PATCH/DELETE before asserting
it 'redirects with flash on success' do
  post users_path, params: { user: valid_params }

  expect(response).to redirect_to(users_path)
  follow_redirect!
  expect(inertia).to have_flash(notice: 'User created!')
end

it 'returns validation errors on failure' do
  post users_path, params: { user: { name: '' } }

  follow_redirect!
  expect(inertia).to have_props(errors: hash_including('name' => anything))
end

Test Shared Props

Shared props from inertiashare are included in inertia.props. The inertia helper is available in type: :request specs after requiring inertiarails/rspec:

it 'includes shared auth data' do
  sign_in(user)
  get dashboard_path

  expect(inertia).to have_props(
    auth: hash_including(user: hash_including(id: user.id))
  )
end

it 'excludes auth data for unauthenticated users' do
  get dashboard_path

  expect(inertia).to have_props(auth: hash_including(user: nil))
end

Test Deferred Props

it 'defers expensive analytics data' do
  get dashboard_path

  expect(inertia).to have_deferred_props(:analytics, :statistics)
  expect(inertia).to have_deferred_props(:slow_data, group: :slow)
end

Partial Reload Helpers

it 'supports partial reload' do
  get users_path

  # Simulate partial reload — only fetch specific props
  inertia_reload_only(:users, :pagination)

  # Or exclude specific props
  inertia_reload_except(:expensive_stats)

  # Load deferred props
  inertia_load_deferred_props(:default)
  inertia_load_deferred_props # loads all groups
end

Test External Redirects (inertia_location)

it 'redirects to Stripe via inertia_location' do
  post checkout_path

  # inertia_location returns 409 with X-Inertia-Location header
  expect(response).to have_http_status(:conflict)
  expect(response.headers['X-Inertia-Location']).to match(/stripe\.com/)
end

NEVER Test These

• Inertia framework behavior — don't test that <Form> sends CSRF tokens or that router.visit works. Test YOUR controller logic.
• Exact prop structure — use have_props(users: satisfy { ... }), not deep equality on full JSON. Brittle tests break when you add a column.
• Flash without followredirect! — after POST/PATCH/DELETE with redirect, you MUST followredirect! before asserting flash or props. Without it you're asserting against the 302, not the page.
• Deferred prop values on initial load — deferred props are nil in the initial response because they're fetched in a separate request after page render. Use havedeferredprops(:key) to verify they're registered, or inertialoaddeferred_props to resolve them in tests.
• Mocked Inertia responses — use type: :request specs that exercise the full stack. type: :controller specs with assigns don't work because Inertia uses a custom render pipeline that only executes in the full request cycle.

Direct Access (use matchers above when possible)

inertia.component       # => 'users/index'
inertia.props           # => { users: [...] }
inertia.props[:users]   # direct prop access
inertia.flash           # => { notice: 'Created!' }
inertia.deferred_props  # => { default: [:analytics], slow: [:report] }

Related Skills

• Controller patterns → inertia-rails-controllers (prop types, flash, PRG)
• Form flows → inertia-rails-forms (submission, validation)
• Deferred/shared props → inertia-rails-pages (Deferred, usePage)

References

MANDATORY — READ ENTIRE FILE when writing Minitest tests (not RSpec): [references/minitest.md](references/minitest.md) (~40 lines) — Minitest assertions equivalent to the RSpec matchers above.

Do NOT load minitest.md for RSpec projects — the matchers above are all you need.