Rspec | メソッドチェーンの検証方法 ( expect_any_instance_of ) ref: http://qiita.com/Yinaura/items/678c5163c0aa6cba6272

file2.txt

{ name: 'John' }.to_a.class # => Array

hahs_to_array_spec.rb

require 'spec_helper'

describe  do
  it do
    expect_any_instance_of(Hash).to receive(:to_a)
    { name: 'John' }.to_a
  end
end

hash_to_array_to_hash.rb

require 'spec_helper'

describe  do
  it do
    expect_any_instance_of(Hash).to receive(:to_a)
    expect_any_instance_of(Array).to receive(:to_s)
    { name: 'John' }.to_a.to_s
  end
end