RSpec Testing Skill

Core Patterns

Basic Test

RSpec.describe Calculator do
  subject(:calculator) { described_class.new }

  describe '#add' do
    it 'adds two positive numbers' do
      expect(calculator.add(2, 3)).to eq(5)
    end

    it 'handles negative numbers' do
      expect(calculator.add(-1, 1)).to eq(0)
    end
  end

  describe '#divide' do
    it 'divides evenly' do
      expect(calculator.divide(10, 2)).to eq(5)
    end

    it 'raises on zero divisor' do
      expect { calculator.divide(10, 0) }.to raise_error(ZeroDivisionError)
    end
  end
end

Matchers

# Equality
expect(actual).to eq(expected)           # ==
expect(actual).to eql(expected)          # eql?
expect(actual).to equal(expected)        # equal? (same object)
expect(actual).to be(expected)           # equal?

# Comparison
expect(value).to be > 5
expect(value).to be_between(1, 10).inclusive

# Truthiness
expect(value).to be_truthy
expect(value).to be_falsey
expect(value).to be_nil

# Collections
expect(array).to include(3)
expect(array).to contain_exactly(1, 2, 3)
expect(array).to match_array([3, 1, 2])
expect(hash).to include(name: 'Alice')

# Strings
expect(str).to include('hello')
expect(str).to start_with('He')
expect(str).to match(/\d+/)

# Types
expect(obj).to be_a(String)
expect(obj).to be_an_instance_of(MyClass)

# Exceptions
expect { method }.to raise_error(StandardError)
expect { method }.to raise_error(StandardError, /message/)

# Change
expect { user.activate }.to change(user, :active).from(false).to(true)
expect { list.push(1) }.to change(list, :size).by(1)

Hooks and Let

RSpec.describe UserService do
  let(:repo) { instance_double(UserRepository) }
  let(:service) { described_class.new(repo) }

  before(:each) do
    allow(repo).to receive(:save).and_return(true)
  end

  after(:each) { cleanup }
  before(:all) { setup_database }
  after(:all) { teardown_database }

  context 'when creating a user' do
    it 'saves to repository' do
      service.create('Alice', 'alice@test.com')
      expect(repo).to have_received(:save).once
    end
  end
end

Mocking and Stubbing

# Doubles
user = double('User', name: 'Alice', email: 'alice@test.com')
user = instance_double(User, name: 'Alice')

# Stubs
allow(service).to receive(:fetch).and_return(data)
allow(service).to receive(:fetch).with('id').and_return(user)

# Expectations
expect(service).to receive(:save).once
expect(service).to receive(:notify).with('alice@test.com')
expect(service).not_to receive(:delete)

Shared Examples

RSpec.shared_examples 'a valid model' do
  it { is_expected.to be_valid }
  it { is_expected.to respond_to(:save) }
end

RSpec.describe User do
  subject { described_class.new(name: 'Alice') }
  it_behaves_like 'a valid model'
end

Anti-Patterns

Bad	Good	Why
before with heavy setup	let (lazy)	Only evaluates when used
No contexts	context 'when...'	Clear scenarios
Instance variables	let blocks	Cleaner, lazier
should syntax	expect().to	Modern RSpec

Setup: gem install rspec then rspec --init

Run: bundle exec rspec or rspec spec/models/user_spec.rb

Config: .rspec file with --format documentation --color

Deep Patterns

For advanced patterns, debugging guides, CI/CD integration, and best practices, see reference/playbook.md.