validate_not_nil matcher (sketch)

00_README.md

You can use this matcher like so:

RSpec.describe User, type: :model do
  it { is_expected.to validate_not_nil(:favorite_numbers) }
end

01_rails_helper.rb

# do this, or just uncomment the line that requires support files
require_relative 'support/matchers/validate_not_nil_matcher'

RSpec.configure do |config|
  config.include Matchers, type: :model
end

02_validate_not_nil_matcher.rb

# spec/support/matchers/validate_not_nil_matcher.rb

module Matchers
  def validate_not_nil(attribute_name)
    ValidateNotNilMatcher.new(attribute_name)
  end
  
  class ValidateNotNilMatcher
    def initialize(attribute_name)
      @attribute_name = attribute_name
      @submatchers = [
        disallow_value(nil).for(attribute_name),
        allow_value([]).for(attribute_name),
        allow_value(["something"]).for(attribute_name)
      ]
    end

    def matches?(record)
      @record = record
      first_failing_submatcher.nil?
    end

    def does_not_match?(record)
      @record = record
      first_passing_submatcher.nil?
    end

    def failure_message
      first_failing_submatcher.failure_message
    end

    def failure_message_when_negated
      first_passing_submatcher.failure_message_when_negated
    end

    private

    attr_reader :attribute_name, :submatchers, :record

    def allow_value(value)
      # Using this class like this is the same as using the `allow_value` matcher.
      Shoulda::Matchers::ActiveModel::AllowValueMatcher.new(value)
    end

    def disallow_value(value)
      # The gem doesn't ship with a `disallow_value` matcher, but it does have a
      # complement to AllowValueMatcher which such a matcher would probably use,
      # if it did exist. Technically this is a private API, but I don't plan on
      # removing this any time soon.
      Shoulda::Matchers::ActiveModel::DisallowValueMatcher.new(value)
    end

    def first_failing_submatcher
      @first_failing_submatcher ||= submatchers.find do |submatcher|
        !submatcher.matches?(record)
      end
    end

    def first_passing_submatcher
      @first_passing_submatcher ||= submatchers.find do |submatcher|
        !submatcher.does_not_match?(record)
      end
    end
  end
end