Testing

If you use end-to-end tools like Capybara or client-side frameworks like Vitest, those work with Inertia out of the box. This page covers endpoint tests — testing the Inertia responses from your Rails backend.

Setup

Available since:inertia_rails:3.17.0

Inertia Rails provides test helpers for both RSpec and Minitest.

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

RSpec helpers are automatically available in all request specs. Minitest helpers are automatically included in ActionDispatch::IntegrationTest.

Assertions

Both RSpec and Minitest provide matchers/assertions for testing Inertia responses. In RSpec, negation is done with not_to.

The inertia helper gives you direct access to inertia.props, inertia.component, inertia.view_data, inertia.flash, and inertia.deferred_props.

Description	RSpec	Minitest
Inertia response	be_inertia_response	assert_inertia_response / refute_inertia_response
Component name	render_component	assert_inertia_component / refute_inertia_component
Props (partial match)	have_props	assert_inertia_props / refute_inertia_props
Props (exact match)	have_exact_props	assert_inertia_props_equal / refute_inertia_props_equal
Prop key absent	have_no_prop	assert_no_inertia_prop
View data (partial match)	have_view_data	assert_inertia_view_data / refute_inertia_view_data
View data (exact match)	have_exact_view_data	assert_inertia_view_data_equal / refute_inertia_view_data_equal
View data key absent	have_no_view_data	assert_no_inertia_view_data
Flash (partial match)	have_flash	assert_inertia_flash / refute_inertia_flash
Flash (exact match)	have_exact_flash	assert_inertia_flash_equal / refute_inertia_flash_equal
Flash key absent	have_no_flash	assert_no_inertia_flash
Deferred props	have_deferred_props	assert_inertia_deferred_props / refute_inertia_deferred_props

# spec/requests/events_spec.rb
RSpec.describe '/events' do
  describe '#index' do
    let!(:event) { Event.create!(title: 'Rails World', start_date: '2026-09-23', description: 'Annual Ruby on Rails conference') }

    it 'renders inertia component' do
      get events_path

      expect(inertia).to be_inertia_response
      expect(inertia).to render_component 'events/index'
      expect(inertia).to have_props(title: 'Rails World')
      expect(inertia).to have_exact_props(title: 'Rails World', start_date: '2026-09-23', description: 'Annual Ruby on Rails conference')

      # Props support both symbol and string keys
      expect(inertia.props[:title]).to eq 'Rails World'
      expect(inertia.props['title']).to eq 'Rails World'

      expect(inertia).to have_view_data(timezone: 'UTC')
      expect(inertia).to have_exact_view_data(timezone: 'UTC')
      expect(inertia.view_data[:timezone]).to eq 'UTC'

      expect(inertia).to have_no_prop(:secret)
    end
  end
end

Common testing tasks

Test flash messages

Inertia Rails automatically shares flash data with your frontend.

RSpec.describe '/events' do
  it 'shows flash message after create' do
    post events_path, params: { event: { title: 'New Event' } }

    expect(inertia).to have_flash(notice: 'Event created!')
    expect(inertia).to have_exact_flash(notice: 'Event created!')
    expect(inertia.flash[:notice]).to eq 'Event created!'
    expect(inertia).to have_no_flash(:alert)
  end
end

Test validation errors

Validation errors are shared as props automatically when using redirect_to with inertia_errors. Assert them on the errors key.

RSpec.describe '/events' do
  it 'returns validation errors' do
    post events_path, params: { event: { title: '' } }

    expect(inertia).to render_component 'events/new'
    expect(inertia).to have_props(errors: { title: ["can't be blank"] })
  end
end

Test redirects

After a redirect, use follow_redirect! and assert the resulting Inertia response.

RSpec.describe '/events' do
  it 'redirects after create' do
    post events_path, params: { event: { title: 'Conference' } }
    follow_redirect!

    expect(inertia).to render_component 'events/show'
    expect(inertia).to have_flash(notice: 'Event created!')
  end
end

Test deferred props

Deferred props are excluded from the initial page load and fetched in a subsequent request.

RSpec.describe '/events' do
  it 'defers expensive data' do
    get events_path

    expect(inertia).to have_deferred_props
    expect(inertia).to have_deferred_props(:analytics)
    expect(inertia).to have_deferred_props(:analytics, :statistics)

    # Check a specific group
    expect(inertia).to have_deferred_props(:other_data, group: :slow)

    expect(inertia.deferred_props[:default]).to include('analytics')
    expect(inertia.props[:analytics]).to be_nil
  end
end

Test partial reloads

Use inertia_reload_only, inertia_reload_except, and inertia_load_deferred_props to simulate partial reloads and deferred prop loading.

RSpec.describe '/events' do
  it 'supports partial reloads' do
    get events_path

    inertia_reload_only(:analytics, :statistics)
    expect(inertia.props[:analytics]).to be_present

    inertia_reload_except(:expensive_data)

    # Load deferred props by group
    inertia_load_deferred_props(:default)

    # Load all deferred props
    inertia_load_deferred_props
  end
end

Configuration

evaluate_optional_props

Available since:inertia_rails:3.18.0

By default, optional and deferred props are excluded on first load — just like in production. This means inertia.props[:my_optional] returns nil unless you simulate a partial reload.

To have these props evaluated on first load in tests, enable evaluate_optional_props:

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

InertiaRails::Testing.evaluate_optional_props = true

Optional and deferred props are then included in inertia.props on first load:

get events_path

expect(inertia.props[:analytics]).to be_present
expect(inertia.props[:statistics]).to eq({ views: 100 })

You can also toggle this setting per-test:

around do |example|
  InertiaRails::Testing.evaluate_optional_props = true
  example.run
ensure
  InertiaRails::Testing.evaluate_optional_props = false
end

WARNING

When evaluate_optional_props is enabled, deferred props will appear in inertia.props but will still be listed in inertia.deferred_props. Partial reload behaviour is unaffected — this setting only changes first-load behaviour.