RSpec custom matchers

rspec_custom_matcher.rb

require 'bundler/inline'

gemfile do
  source 'https://rubygems.org'
  gem 'rspec'
end

require 'rspec/autorun'

class Car
  attr_reader :make, :model, :year, :doors

  def initialize(make: 'Chevrolet', model: 'Impala', year: 1967, doors: 2)
    @make = make
    @model = model
    @year = year
    @doors = doors
  end
end

RSpec.configure do |config|
  config.expect_with :rspec do |c|
    c.include_chain_clauses_in_custom_matcher_descriptions = true
  end
end

RSpec.describe Car do
  specify do
    expect(Car.new).to be_made_by('Chevrolet')
      .and have_model('Impala')
      .and have_been_made_in(1967)
      .and have_two_doors
  end

  specify do
    expect(Car.new(doors: 4)).to not_be_made_by('Nissan')
      .and not_have_model('Skyline')
      .and not_have_been_made_in(2010)
      .and not_have_two_doors
  end

  specify do
    car = Car.new(year: 1980)
    expect(car).to have_been_made_after(1970)
      .and_before(1990)
  end

  context 'when using information from the context' do
    let(:today) do
      require 'date'
      Date.ordinal(2019, -1) # 31/12/2019
    end

    specify do
      car = Car.new(year: 1960)
      expect(car).to be_older_than(1980)
        .and be_older_than(40).years
    end
  end

  matcher :be_older_than do
    match do |actual|
      if @older_than_year
        today - actual.year > expected
      else
        have_been_made_before(expected)
      end
    end

    chain :years do
      @older_than_year = true
    end
  end

  matcher :have_been_made_before do
    match do |actual|
      actual.year < expected
    end
  end

  matcher :have_been_made_after do
    match do |actual|
      made_after = actual.year > expected

      if @before_year
        made_after && actual.year < @before_year
      else
        made_after
      end
    end

    match_when_negated do |actual|
      if @before_year
        fail ArgumentError, "You can't chain `and_before` when using negated version"
      end

      actual.year <= expected
    end

    chain :and_before do |before_year|
      @before_year = before_year
    end

    description do
      desc = "be manufactured after #{expected}"
      desc << " and before #{@before_year}" if @before_year
    end

    failure_message do |actual|
      message = "Expected #{actual} to have been made after #{expected}"
      message << " and before #{@before_year}" if @before_year
      message << " but it was made in #{actual.year}."
    end

    RSpec::Matchers.define_negated_matcher :not_have_been_made_after, :have_been_made_after
  end

  matcher :be_made_by do
    match do |actual|
      actual.make == expected
    end

    RSpec::Matchers.define_negated_matcher :not_be_made_by, :be_made_by
  end

  matcher :have_model do
    match do |actual|
      actual.model == expected
    end

    RSpec::Matchers.define_negated_matcher :not_have_model, :have_model
  end

  matcher :have_been_made_in do
    match do |actual|
      actual.year == expected
    end

    RSpec::Matchers.define_negated_matcher :not_have_been_made_in, :have_been_made_in
  end

  matcher :have_two_doors do
    match do |actual|
      actual.doors == 2
    end

    RSpec::Matchers.define_negated_matcher :not_have_two_doors, :have_two_doors
  end
end