Redefining a stubbed method, using Mocha

class_method_double.rb

require 'minitest/spec'
require 'mocha/setup'
require 'minitest/autorun'

class MyClass

  class << self
    attr_accessor :bar
  end

  def self.foo
    self.bar = :baz
  end

end

describe "MyClass" do

  subject do
    MyClass.tap { MyClass.bar = nil }
  end

  it "will stub out foo" do
    subject.stubs(:foo).returns(:quux)

    subject.foo.must_equal :quux
  end

  it "doesn't set bar" do
    subject.stubs(:foo).returns(:quux)

    subject.foo

    subject.bar.must_be_nil
  end

  it "can be replaced" do
    subject.stubs(:foo)

    def subject.foo
      self.bar = :boosh
    end

    subject.foo

    subject.bar.must_equal :boosh
  end

  it "replacement isn't permanent" do
    subject.stubs(:foo)

    def subject.foo
      self.bar = :boosh
    end

    subject.unstub(:foo)

    subject.foo

    subject.bar.must_equal :baz
  end

end