Feature: Using an instance double

  An `instance_double` is the most common type of verifying double. It takes a class name or
  object as its first argument, then verifies that any methods being stubbed would be present
  on an _instance_ of that class. If any argument matchers are specified, it also verifies that the
  number of arguments is correct.

  For methods handled by `method_missing`, see [dynamic classes](./dynamic-classes).

  Background:
    Given a file named "app/models/user.rb" with:
      """ruby
      class User < Struct.new(:notifier)
        def suspend!
          notifier.notify("suspended as")
        end
      end
      """

    Given a file named "spec/unit_helper.rb" with:
      """ruby
      $LOAD_PATH.unshift("app/models")
      """

    Given a file named "spec/spec_helper.rb" with:
      """ruby
      require 'unit_helper'

      require 'user'
      require 'console_notifier'

      RSpec.configure do |config|
        config.mock_with :rspec do |mocks|

          # This option should be set when all dependencies are being loaded
          # before a spec run, as is the case in a typical spec helper. It will
          # cause any verifying double instantiation for a class that does not
          # exist to raise, protecting against incorrectly spelt names.
          mocks.verify_doubled_constant_names = true

        end
      end
      """

    Given a file named "spec/unit/user_spec.rb" with:
      """ruby
      require 'unit_helper'

      require 'user'

      RSpec.describe User, '#suspend!' do
        it 'notifies the console' do
          notifier = instance_double("ConsoleNotifier")

          expect(notifier).to receive(:notify).with("suspended as")

          user = User.new(notifier)
          user.suspend!
        end
      end
      """

  Scenario: spec passes in isolation
    When I run `rspec spec/unit/user_spec.rb`
    Then the examples should all pass

  Scenario: spec passes with dependencies loaded and method implemented
    Given a file named "app/models/console_notifier.rb" with:
      """ruby
      class ConsoleNotifier
        def notify(msg)
          puts message
        end
      end
      """

    When I run `rspec -r./spec/spec_helper spec/unit/user_spec.rb`
    Then the examples should all pass

  Scenario: spec fails with dependencies loaded and method unimplemented
    Given a file named "app/models/console_notifier.rb" with:
      """ruby
      class ConsoleNotifier
      end
      """
    When I run `rspec -r./spec/spec_helper spec/unit/user_spec.rb`
    Then the output should contain "1 example, 1 failure"
    And the output should contain "ConsoleNotifier does not implement:"

  Scenario: spec fails with dependencies loaded and incorrect arity
    Given a file named "app/models/console_notifier.rb" with:
      """ruby
      class ConsoleNotifier
        def notify(msg, color)
          puts color + message
        end
      end
      """
    When I run `rspec -r./spec/spec_helper spec/unit/user_spec.rb`
    Then the output should contain "1 example, 1 failure"
    And the output should contain "Wrong number of arguments."