RSpec Boolean Matcher Shared Example with Shoulda Matchers

rspec_shared_example_with_shoulda_matchers_for_booleans.rb

# Shared specs for models with the `:validates_inclusion_of` validators, where
#  Boolean values are specified. This is for use cases where Booleans are  used
#  in non-null DB columns, and validation errors need to be returned to actors
#  attempting to store a NULL value (e.g., a IoT unit's firmware uploading a
#  NULL value for an On/Off sensor reading).
# Additionally, `shoulda` will complain if `validate_inclusion_of` is used
#  with the Booleans, and instead of turning off warnings, its best to just
#  approach these specs differently. See
#  [this github comment](https://github.com/thoughtbot/shoulda-matchers/issues/922#issuecomment-225752673)
#  for more info.
RSpec.shared_examples :validates_boolean_model do |attribute_name, options|

  it { is_expected.to allow_values(true, false).for(attribute_name.to_sym) }
  it { is_expected.not_to allow_value(nil).for(attribute_name.to_sym) }

  it {
    expect(
      described_class.new(attribute_name.to_sym => nil).errors_on(attribute_name.to_sym)
    ).to include(options[:bool_validation_message])
  } if options[:bool_validation_message]

end

This is an RSpec matcher to be used when you have robots uploading data (firmware, raspberry pi, IoT boards, etc), and you would like to express a specification in your data models that strictly true or false values are the only acceptable input.