Send mail matcher

send_mail.rb

# frozen_string_literal: true

# Source: https://gist.github.com/ka8725/6053d55be74f15b53cabfc3ac4dc99df
# Installation: put this file into spec/support/matchers/ folder.

# Simple matcher that allows checking of an email was sent during an example run.
#
# @example Positive expectation
#   expect { action }.to send_email
#
# @example Negative expectations
#   expect { action }.not_to send_email
#   expect { action }.to not_send_email
#
# @example More precise expectation with attributes to match
#   expect { action }.to send_email(to: '[email protected]', subject: 'Confirm email')
#
RSpec::Matchers.define :send_email do |criteria = {}|
  match do |block|
    @init_criteria = criteria
    define_matched_emails(block)
    @matched_emails.size == 1
  end

  failure_message do
    if multiple_match?
      'More than 1 matching emails were sent.'
    else
      super()
    end
  end

  match_when_negated do |block|
    define_matched_emails(block)
    @matched_emails.size.zero?
  end

  diffable

  supports_block_expectations

  private

  def define_matched_emails(block)
    before = deliveries

    block.call

    after = deliveries

    @diff = after - before
    @matched_emails = select_matching(@diff)
  end

  def deliveries
    ActionMailer::Base.deliveries.clone
  end

  def select_matching(emails)
    criteria.empty? ? emails : emails.select(&method(:matched_email?))
  end

  def matched_email?(email)
    # `values_match?` is RSpec's comparison API, supporting value matchers like
    # `hash_including`, `ends_with` and so on.
    criteria.all? do |attr, expected|
      values_match?(expected, email.public_send(attr))
    end
  end

  def criteria
    @criteria ||=
      if init_criteria.key?(:to)
        { **init_criteria, to: Array(init_criteria[:to]) }
      else
        init_criteria
      end
  end

  def init_criteria
    @init_criteria ||= {}
  end

  def multiple_match?
    @matched_emails.many?
  end
end

RSpec::Matchers.define_negated_matcher :not_send_email, :send_email