Rspec で クラスメソッドのスタブを作る方法 ref: http://qiita.com/Yinaura/items/dfc09fd6d4b953181e2d

example.rb

class Example
  def self.class_method
    'This is real class method'
  end
end

test_spec.rb

require 'spec_helper'

describe do
  before do
    allow(Example).to receive(:class_method).and_return('This is stub class method')
  end

  it do
    p Example.class_method
  end
end