describe, Matchers, let & Context

A Basic Spec

RSpec.describe User do
  subject { described_class.new(name: 'Ada') }

  describe '#valid?' do
    context 'when name is present' do
      it { is_expected.to be_valid }
    end

    context 'when name is missing' do
      let(:user) { described_class.new(name: nil) }

      it 'is invalid' do
        expect(user).not_to be_valid
      end
    end
  end
end

describe groups examples; it defines one. context is an alias for describe, conventionally used for state/condition groupings. subject + is_expected enables concise one-liners. described_class refers to the class being described without hardcoding its name — stays in sync if the class is renamed.

eq vs. equal, and let's Laziness

expect(value).to eq(other)      # value equality (==)
expect(value).to equal(other)   # reference identity

let(:user) { User.create!(name: 'Ada') }  # lazy — only runs if referenced
before { @user = User.create!(name: 'Ada') }  # eager — runs for every example

Setup & Teardown

before(:each)/after(:each) run per example; before(:all)/after(:all) run once per group. expect syntax (expect(x).to matcher) is the modern default, replacing the older monkey-patched should syntax (x.should matcher).