Effective Testing with RSpec 3

Negating Matchers

In ​Putting the Pieces Together​, we saw RSpec’s not_to and to_not methods, which specify that a given condition should not hold:

12-creating-custom-matchers/05/custom_matchers.rb

expect(correct_grammar).to_not split_infinitives

If you find yourself doing this over and over again, you can define a negated matcher that you’d use like so:

12-creating-custom-matchers/05/custom_matchers.rb

expect(correct_grammar).to avoid_splitting_infinitives

It’s easy to create your own negated matcher. All you have to do is call define_negated_matcher:

12-creating-custom-matchers/05/custom_matchers.rb

RSpec::Matchers.define_negated_matcher :avoid_splitting_infinitives,
                                       :split_infinitives

As with alias_matcher, you pass the name of ...