Project: Rspec-mocks

Publisher: rspec-pritesh

Using a class double

class_double is provided as a complement to instance_double with the difference that it
verifies class methods on the given class rather than instance methods.

In addition, it also provides a convenience method as_stubbed_const to replace concrete
classes with the defined double. See mutating constants for more details.

Note: class_double can be used for modules as well. We chose to stick with the
class_double terminology because the methods a class_double verifies against are
commonly called "class methods", not "module methods", even when working with a module.

Background

Given

a file named "lib/user.rb" with:

class User
  def suspend!
    ConsoleNotifier.notify("suspended as")
  end
end

Given

a file named "lib/console_notifier.rb" with:

class ConsoleNotifier
  MAX_WIDTH = 80

  def self.notify(message)
    puts message
  end
end

Given

a file named "spec/user_spec.rb" with:

require 'user'
require 'console_notifier'

RSpec.describe User, '#suspend!' do
  it 'notifies the console' do
    notifier = class_double("ConsoleNotifier").
      as_stubbed_const(:transfer_nested_constants => true)

    expect(notifier).to receive(:notify).with("suspended as")
    expect(ConsoleNotifier::MAX_WIDTH).to eq(80)

    user = User.new
    user.suspend!
  end
end

Scenarios

replacing existing constants

When: I run rspec spec/user_spec.rb
Then: the examples should all pass

renaming `ConsoleNotifier.notify` to `send_notification`

Given

a file named "lib/console_notifier.rb" with:

class ConsoleNotifier
  MAX_WIDTH = 80

  def self.send_notification(message)
    puts message
  end
end

When

I run rspec spec/user_spec.rb

Then

the output should contain "1 example, 1 failure"

And

the output should contain "ConsoleNotifier does not implement:"

Last published over 7 years ago by Pritesh Jain.

Using a class double

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