Allow instance_double's to pass class equivalence checks (see https://github.com/rspec/rspec-mocks/issues/794)

verified_double_extensions.rb

module VerifiedDoubleExtensions
  CLASS_EQUIVALENCE_FUNCTIONS = %i[is_a? kind_of? instance_of?].freeze

  def verified_double(klass, *args)
    instance_double(klass, *args).tap do |dbl|
      CLASS_EQUIVALENCE_FUNCTIONS.each do |fn|
        allow(dbl).to receive(fn) do |*fn_args|
          klass.allocate.send(fn, *fn_args)
        end
      end
      allow(klass).to receive(:===).and_call_original # do the normal thing by default
      allow(klass).to receive(:===).with(dbl).and_return true
    end
  end
end

RSpec.configure do |c|
  c.include VerifiedDoubleExtensions
end