RSpec Core Fundamentals

RSpec is a behavior-driven development (BDD) testing framework for Ruby. This skill covers the core DSL for structuring and writing specs.

Example Group Structure

describe and context

Use describe for the thing being tested (class, method, behavior). Use context for different scenarios or states:

RSpec.describe User do
  describe "#full_name" do
    context "when user has both names" do
      it "returns first and last name" do
        user = User.new(first_name: "John", last_name: "Doe")
        expect(user.full_name).to eq("John Doe")
      end
    end

    context "when user has no last name" do
      it "returns only first name" do
        user = User.new(first_name: "John", last_name: nil)
        expect(user.full_name).to eq("John")
      end
    end
  end
end

Naming conventions:

describe with class name: RSpec.describe User
describe with method: describe "#instance_method" or describe ".class_method"
context starts with "when", "with", "without", "given": context "when logged in"

it and specify

Use it for individual test cases. The description should complete the sentence "it...":

it "returns the user's email" do
  expect(user.email).to eq("test@example.com")
end

# For complex descriptions, use specify
specify "the total includes tax and shipping" do
  expect(order.total).to eq(110.00)
end

One expectation per example (generally): Each it block should test one behavior. Multiple expectations are acceptable when testing related aspects of a single behavior.

Subject and Let

subject

Defines the primary object under test:

RSpec.describe User do
  subject { User.new(name: "John") }

  it { is_expected.to be_valid }

  # Named subject for clarity
  subject(:user) { User.new(name: "John") }

  it "has the correct name" do
    expect(user.name).to eq("John")
  end
end

let and let!

Use let for lazy-evaluated memoized helpers:

RSpec.describe Order do
  let(:user) { User.create!(name: "John") }
  let(:product) { Product.create!(name: "Widget", price: 10) }
  let(:order) { Order.new(user: user, product: product) }

  it "calculates total correctly" do
    expect(order.total).to eq(10)
  end
end

let vs let!:

let - Lazy evaluation, created when first referenced
let! - Eager evaluation, created before each example

let(:user) { User.create!(name: "John") }    # Created only if referenced
let!(:admin) { User.create!(admin: true) }   # Always created before each test

When to use let!:

Database records that must exist for callbacks/associations
Setup that has side effects needed by other code
When order of creation matters

Hooks

before and after

Execute code before or after examples:

RSpec.describe User do
  before(:each) do    # or just `before do`
    @user = User.new
  end

  after(:each) do
    # Cleanup after each example
  end

  before(:all) do     # or before(:context)
    # Run once before all examples in this group
    # Be careful: shared state between examples
  end

  after(:all) do
    # Run once after all examples
  end
end

Hook execution order:

before(:all) - once per describe/context block
before(:each) - before every example
The example runs
after(:each) - after every example
after(:all) - once after all examples

around

Wrap examples with custom logic:

around(:each) do |example|
  Timecop.freeze(Time.now) do
    example.run
  end
end

# Useful for database transactions
around(:each) do |example|
  ActiveRecord::Base.transaction do
    example.run
    raise ActiveRecord::Rollback
  end
end

Pending and Skipping

pending

Mark examples as not yet implemented or temporarily broken:

it "sends welcome email" do
  pending "email service not implemented"
  expect(user.send_welcome_email).to be_truthy
end

# Or mark entire example as pending
pending "calculates complex tax" do
  expect(order.tax).to eq(15.00)
end

skip

Skip examples entirely:

it "requires external service", skip: "API not available in test" do
  # This won't run
end

# Conditional skip
it "runs on CI only", skip: !ENV["CI"] do
  # Skipped locally
end

# Skip with xit
xit "not implemented yet" do
  # Skipped
end

Metadata and Filtering

Add metadata to examples and filter runs:

RSpec.describe User, type: :model do
  it "validates email", :slow do
    # Tagged with :slow
  end

  it "processes payment", :integration, timeout: 30 do
    # Multiple tags
  end
end

# Run filtered specs:
# rspec --tag slow
# rspec --tag ~slow  (exclude slow)
# rspec --tag type:model

Focus

Temporarily run only specific examples:

fit "only this test runs" do     # focus + it
  expect(true).to be true
end

fdescribe User do                 # focus + describe
  # Only examples in this block run
end

fcontext "when focused" do        # focus + context
end

Important: Remove focus tags before committing. Configure CI to fail on focus:

# spec/spec_helper.rb
RSpec.configure do |config|
  config.filter_run_when_matching :focus
  config.run_all_when_everything_filtered = true
end

Configuration

spec_helper.rb vs rails_helper.rb

spec_helper.rb - Pure RSpec configuration, no Rails
rails_helper.rb - Rails-specific setup, requires spec_helper

# spec/spec_helper.rb
RSpec.configure do |config|
  config.expect_with :rspec do |expectations|
    expectations.include_chain_clauses_in_custom_matcher_descriptions = true
  end

  config.mock_with :rspec do |mocks|
    mocks.verify_partial_doubles = true
  end

  config.shared_context_metadata_behavior = :apply_to_host_groups
  config.filter_run_when_matching :focus
  config.example_status_persistence_file_path = "spec/examples.txt"
  config.disable_monkey_patching!
  config.order = :random
  Kernel.srand config.seed
end

Best Practices

Describe What, Not How

# Good - describes behavior
it "returns user's full name" do
  expect(user.full_name).to eq("John Doe")
end

# Avoid - describes implementation
it "concatenates first_name and last_name with space" do
  expect(user.full_name).to eq("John Doe")
end

Use Descriptive Context Names

# Good
context "when user is an admin"
context "with valid attributes"
context "without a password"

# Avoid
context "admin case"
context "valid"
context "test 1"

Prefer let Over Instance Variables

# Good
let(:user) { create(:user) }

# Avoid
before { @user = create(:user) }

Keep Examples Independent

Each example should be able to run in isolation. Avoid dependencies between examples.

Additional Resources

Reference Files

For advanced patterns and detailed examples:

references/hooks-deep-dive.md - Comprehensive hook patterns and execution order
references/configuration.md - Full RSpec configuration options

Example Files

Working examples in examples/:

examples/model_spec.rb - Complete model spec example
examples/service_spec.rb - Service object testing patterns

RSpec Core