RSpec::Core Cheat Sheet

RSpec.describe 'an array of animals' do
  let(:animal_array) { [:cat, :dog, :mule] }

  it 'has three animals' do
    expect(animal_array.size).to eq(3)
  end

  context 'mutation' do
    after { expect(animal_array.size).not_to eq(3) }

    it 'can have animals added' do
      animal_array << :cow
      expect(animal_array).to eq([:cat, :dog, :mule, :cow])
    end

    it 'can have animals removed' do
      animal_array.pop
      expect(animal_array).to eq([:cat, :dog])
    end
  end
end

RSpec.describe 'Uses of `let`' do
  let(:random_number) { rand }
  let(:lazy_creation_time) { Time.now }
  let!(:eager_creation_time) { Time.now }

  it 'memoizes values' do
    first = random_number
    second = random_number
    expect(first).to be(second)
  end

  it 'creates the value lazily' do
    start_of_test = Time.now
    expect(lazy_creation_time).to be > start_of_test
  end

  it 'creates the value eagerly using `let!`' do
    start_of_test = Time.now
    expect(eager_creation_time).to be < start_of_test
  end
end

RSpec.describe Array do
  it 'provides methods based on the `RSpec.describe` argument' do
    # described_class = Array
    expect(described_class).to be(Array)
    # subject = described_class.new
    expect(subject).to eq(Array.new)
    # is_expected = expect(subject)
    is_expected.to eq(Array.new)
  end

  context 'explicitly defined subject' do
    # subject can be manually defined
    subject { [1,2,3] }
    it 'is not empty' do
      is_expected.not_to be_empty
    end
  end

  context 'can be named' do
    # you can provide a name, just like `let`
    subject(:bananas) { [4,5,6] }
    it 'can be called by name' do
     expect(bananas.first).to eq(4)
    end
  end
end

RSpec.describe 'Hooks' do
  order = []

  before(:all) { order << 'before(:all)' }
  before       { order << 'before' }
  after        { order << 'after' }
  after(:all)  { order << 'after(:all)'; puts order }

  around do |test|
    order << 'around, pre'
    test.call
    order << 'around, post'
  end

  it 'runs first test' do
    order << 'first test'
  end

  it 'runs second test' do
    order << 'second test'
  end
end

RSpec.describe 'Ways to skip tests' do
  it 'is skipped because it has no body'

  skip 'uses `skip` instead of `it`' do
  end

  xit 'uses `xit` instead of `it`' do
  end

  it 'has `skip` in the body' do
    skip
  end

  xcontext 'uses `xcontext` to skip a group of tests' do
    it 'wont run' do; end
    it 'wont run either' do; end
  end
end

RSpec.describe 'Ways to mark failing tests as "pending"' do
  pending 'has a failing expectation' do
    expect(1).to eq(2)
  end

  it 'has `pending` in the body' do
    pending('reason goes here')
    expect(1).to eq(2)
  end

  pending 'tells you if a pending test has been fixed' do
    # Pending tests are supposed to fail. This test passes,
    # so RSpec will give an error saying that this pending
    # test has been fixed.
    expect(2).to eq(2)
  end
end

RSpec.describe 'Alternate syntax' do
  example_group 'alernative to "context"' do
    example 'alternative to "it"' do
      expect(2).to eq(2)
    end
  end

  describe 'alternative to "context"' do
    specify 'alternative to "it"' do
      expect(2).to eq(2)
    end
  end
end

RSpec.describe 'Defining methods' do
  def my_helper_method(name)
    "Hello #{name}, you just got helped!"
  end

  it 'uses my_helper_method' do
    message = my_helper_method('Susan')
    expect(message).to eq('Hello Susan, you just got helped!')
  end

  context 'within a context group' do
    it 'can still use my_helper_method' do
      message = my_helper_method('Tom')
      expect(message).to eq('Hello Tom, you just got helped!')
    end
  end
end

RSpec.shared_examples 'acts like non-nil array' do
  it 'has a size' do
    expect(subject.size).to be > 0
  end

  it 'has has non-nil values for each index' do
    subject.size.times do |index|
      expect(subject[index]).not_to be_nil
    end
  end
end

RSpec.describe 'A real array' do
  include_examples 'acts like non-nil array' do
    subject { ['zero', 'one', 'two'] }
  end
end

RSpec.describe 'A hash with integer keys' do
  include_examples 'acts like non-nil array' do
    subject { Hash[0 => 'zero', 1 => 'one', 2 => 'two'] }
  end
end

RSpec.shared_context 'test timing' do
  around do |test|
    start_time = Time.now
    test.call
    end_time = Time.now
    puts "Test ran in #{end_time - start_time} seconds"
  end
end

RSpec.describe 'big array' do
  include_context 'test timing'

  it 'has lots of elements' do
    big_array = (1..1_000_000).to_a
    expect(big_array.size).to eq(1_000_000)
  end
end