Alternate implementation for https://thomasleecopeland.com/2018/02/12/increment-decrement-matcher.html

increment_and_decrement.rb

module IncrementAndDecrement
  def increment(&block)
    matcher = change(&block).by(1)
    RSpec::Matchers::AliasedMatcher.new(matcher, lambda do |desc|
      desc.gsub("changed", "incremented").gsub("change", "increment")
    end)
  end

  def decrement(&block)
    matcher = change(&block).by(-1)
    RSpec::Matchers::AliasedMatcher.new(matcher, lambda do |desc|
      desc.gsub("changed", "decremented").gsub("change", "decrement").gsub("-", "")
    end)
  end
end

RSpec.configure do |c|
  c.include IncrementAndDecrement
end

Brilliant! That's a big improvement, thank you Myron! Post updated.