Fixing an issue with a spoiling of the object singleton classes

[alekseyl]

.stub method defined in minitest/mock executing an alias_method against singleton_class under the hood.
Running an alias_method over a singleton_class without running a 'remove_method' later will keep singleton_class 'dirty' and running undef_method might clear more than needed.

Usually this will not lead to any consequences, but if you are stubbing methods of a global objects and trying to enrich functionality of their ancestors chain 'after' the the first stubbing is done, then you might fall into trouble.

Even though the probability for such a case is tiny, it's not 0 and singleton class should be kept clean.

[luke-gru]

What about when you're stubbing a singleton class method instead of an instance method? This would erase the method on the singleton class, unless I'm reading it wrong.

[GermanDZ]

What about when you're stubbing a singleton class method instead of an instance method? This would erase the method on the singleton class, unless I'm reading it wrong.

Also consider these other cases: #811

[alekseyl]

What about when you're stubbing a singleton class method instead of an instance method? This would erase the method on the singleton class, unless I'm reading it wrong.

hm, what about the testcase in the PR:

def test_class_singleton_class_will_not_loose_its_method
    _class = Class.new do
      def self.clean; :dirty end
    end

    _class.stub(:clean, :clean) do |s|
      assert_equal( s.clean, :clean )
    end
    # method is still present and unchanged
    assert_equal( _class.clean, :dirty )
  end

Looks like its covering your concern