Smartest vs RSpec

RSpec is a mature Ruby testing framework with a broad BDD DSL, nested example groups, shared examples, metadata, and a large matcher ecosystem.

Smartest is smaller and more focused. It is designed for tests where setup dependencies should be visible in the test signature and fixture dependency graph.

At a Glance

Concern	RSpec	Smartest
Test shape	describe / context / it blocks	Top-level test("name") blocks
Reusable setup	let, let!, before, helper methods	Class-based fixtures
Dependency visibility	Examples call helper methods from the body	Tests request fixtures with keyword arguments
Setup dependencies	Often expressed by one let calling another	Fixture block keyword arguments
Teardown	after hooks or helper-owned teardown	on_teardown inside the fixture that owns the resource
Best fit	Rich BDD structure and RSpec ecosystem	Explicit pytest-style fixture injection

let Compared With Keyword Fixtures

RSpec let is useful when examples need lazy helper methods:

RSpec

RSpec.describe UserMailer do
  let(:user) { User.new(name: "Alice") }
  let(:mailer) { UserMailer.new(user) }

  it "renders the subject" do
    expect(mailer.subject).to eq("Welcome, Alice")
  end
end

In Smartest, fixtures live in a Smartest::Fixture subclass and tests request them with required keyword arguments:

Smartest

class MailerFixture < Smartest::Fixture
  fixture :user do
    User.new(name: "Alice")
  end

  fixture :mailer do |user:|
    UserMailer.new(user)
  end
end

around_suite do |suite|
  use_fixture MailerFixture
  suite.run
end

test("renders the subject") do |mailer:|
  expect(mailer.subject).to eq("Welcome, Alice")
end

The Smartest test signature shows that the test depends on mailer. The mailer fixture signature shows that it depends on user.

Resource Teardown

RSpec can clean up resources with hooks. Smartest puts teardown next to the resource acquisition:

Smartest

class WebFixture < Smartest::Fixture
  fixture :server do
    server = TestServer.start
    on_teardown { server.stop }
    server
  end

  fixture :client do |server:|
    Client.new(base_url: server.url)
  end
end

This keeps lifecycle ownership local. The fixture that starts server also registers the teardown for server.

Method Stubs

RSpec method stubs often live in before hooks:

RSpec

RSpec.describe Checkout do
  let(:fixed_now) { Time.utc(2026, 1, 1, 0, 0, 0) }

  before do
    allow(Time).to receive(:now).and_return(fixed_now)
  end

  it "uses the fixed time" do
    expect(Checkout.call.created_at).to eq(fixed_now)
  end
end

In Smartest, put the stub in a fixture and request that fixture from tests that depend on it:

Smartest

class TimeFixture < Smartest::Fixture
  fixture :fixed_now do
    fixed_now = Time.utc(2026, 1, 1, 0, 0, 0)
    simple_stub(Time, :now) { fixed_now }
    fixed_now
  end
end

around_suite do |suite|
  use_fixture TimeFixture
  suite.run
end

test("uses the fixed time") do |fixed_now:|
  expect(Checkout.call.created_at).to eq(fixed_now)
end

The fixture signature makes the stubbed dependency explicit, and Smartest resets the method stub from fixture teardown.

For allow_any_instance_of, use simple_stub_any_instance_of:

RSpec

before do
  allow_any_instance_of(ApplicationController)
    .to receive(:current_user)
    .and_return(user1)
end

Smartest

class AuthFixture < Smartest::Fixture
  fixture :user1 do
    create(:user)
  end

  fixture :logged_in_as_user1 do |user1:|
    simple_stub_any_instance_of(ApplicationController, :current_user) { user1 }
    user1
  end
end

test("uses the current user") do |logged_in_as_user1:|
  expect(call_api.user).to eq(logged_in_as_user1)
end

Constant stubs are different from method stubs. Use with_stub_const with a block in a test body, around_test, or around_suite; it is intentionally not a fixture helper because Ruby constants are process-global:

Smartest

test("uses fake payment provider") do
  with_stub_const("AppConfig::PAYMENT_PROVIDER", "fake") do
    expect(Checkout.call).to eq(:paid)
  end
end

When Smartest Is a Good Fit

Smartest is worth considering when:

• tests have setup dependencies that should be visible at the test boundary
• one fixture naturally depends on another fixture
• teardown should live beside the resource setup
• you want a small runner with pytest-style fixture injection for Ruby

RSpec may be a better fit when:

• the suite relies heavily on nested describe and context structure
• shared examples, metadata, or RSpec-specific integrations are central
• the team already benefits from RSpec's matcher and extension ecosystem

Moving One Test at a Time

Smartest does not load test/ or spec/ by default. A project can keep RSpec tests in spec/ while adding Smartest tests under smartest/:

spec/
  user_mailer_spec.rb
smartest/
  test_helper.rb
  fixtures/
    mailer_fixture.rb
  user_mailer_test.rb

Start by moving one setup concept into a fixture class, register it with use_fixture, then make the test request only the fixtures it needs.