How do you use Rspec any_instance stubbing of a Fog::Compute object?

Question

Trying to stub a method of a Fog::Compute object, like so:

describe EtHaproxy::Helpers do
  let(:helpers) { Object.new.extend(EtHaproxy::Helpers) }
  before do
    Fog.mock!
    Fog::Mock.reset

    @fog_conn = Fog::Compute.new(
      provider: 'AWS',
      aws_access_key_id: 'MOCK_ACCESS_KEY',
      aws_secret_access_key: 'MOCK_SECRET_KEY'
    )
    @fog_conn.data[:limits][:addresses] = 25
    2.times do
      @fog_conn.allocate_address('vpc')
    end

    @mock_eips = @fog_conn.addresses.map { |a| a.public_ip }

    Fog::Compute.any_instance.stub(:addresses).and_return(@fog_conn.addresses)
  end

  describe 'any_instance.stub' do
    it 'returns the specified value on any instance of the class' do
      o = Fog::Compute.new(
        provider: 'AWS',
        aws_access_key_id: 'MOCK_ACCESS_KEY',
        aws_secret_access_key: 'MOCK_SECRET_KEY'
      )
      o.addresses.should eq(@fog_conn.addresses)
    end
  end
end

However, upon running this example spec test (lifted from the Relish docs for Rspec 2.14), it fails, stating:

Failure/Error: Fog::Compute.any_instance.stub(:foo).and_return(:return_value)
 NoMethodError:
   undefined method `any_instance' for Fog::Compute:Module

Answer 1

As it turns out, when using Fog.Mock!, Fog creates a convenience layer, and you’re not actually dealing with Fog::Compute, but instead, we end up with Fog::Compute::AWS::Mock. As such, to stub the method, we need to do it like so:

Fog::Compute::AWS::Mock.any_instance.stub(:addresses).and_return(@fog_conn.addresses)

Stubbing on this object results in things working as expected.