Experiments with rspec predicate matchers

predicate_matcher_experiment_spec.rb

require 'spec_helper'

class PredicateMatcherExperiment

  attr_reader :ivar

  def initialize(ivar: nil)
    @ivar = ivar
  end

  def truthy?
    @ivar
  end

  def simple_predicate?
    @ivar
  end

end

describe 'predicate matcher experiment' do

  describe '#truthy?' do

    it 'returns truthy when #ivar is truthy' do
      thing = PredicateMatcherExperiment.new(ivar: :foo)

      # Just checking...
      expect(thing.truthy?).to equal :foo

      expect(thing).to be_truthy
    end

    it 'returns truthy when #ivar is `true`' do
      thing = PredicateMatcherExperiment.new(ivar: true)

      # Just checking...
      expect(thing.truthy?).to equal true

      expect(thing).to be_truthy
    end

    #    Failure/Error: expect(thing).not_to be_truthy
    #
    #  expected: falsey value
    #       got: #<PredicateMatcherExperiment:0x000000010c644fa8 @ivar=nil>
    it 'returns falsey when #ivar is `nil`' do
      thing = PredicateMatcherExperiment.new(ivar: nil)

      # Just checking...
      expect(thing.truthy?).to equal nil

      expect(thing).not_to be_truthy
    end

    #    Failure/Error: expect(thing).not_to be_truthy
    #
    #  expected: falsey value
    #       got: #<PredicateMatcherExperiment:0x000000010c1e1380 @ivar=false>
    it 'returns falsey when #ivar is `false`' do
      thing = PredicateMatcherExperiment.new(ivar: false)

      # Just checking...
      expect(thing.truthy?).to equal false

      expect(thing).not_to be_truthy
    end

  end

  describe '#simple_predicate?' do

    it 'returns truthy when #ivar is truthy' do
      thing = PredicateMatcherExperiment.new(ivar: :foo)

      # Just checking...
      expect(thing.simple_predicate?).to equal :foo

      expect(thing).to be_simple_predicate
    end

    it 'returns truthy when #ivar is `true`' do
      thing = PredicateMatcherExperiment.new(ivar: true)

      # Just checking...
      expect(thing.simple_predicate?).to equal true

      expect(thing).to be_simple_predicate
    end

    it 'returns falsey when #ivar is `nil`' do
      thing = PredicateMatcherExperiment.new(ivar: nil)

      # Just checking...
      expect(thing.simple_predicate?).to equal nil

      expect(thing).not_to be_simple_predicate
    end

    it 'returns falsey when #ivar is `false`' do
      thing = PredicateMatcherExperiment.new(ivar: false)

      # Just checking...
      expect(thing.simple_predicate?).to equal false

      expect(thing).not_to be_simple_predicate
    end

  end

end