def METHOD_NAME(self):
    self._appengine_request.execute.side_effect = [
        # First list_instance response.
        {
            'instances': [{
                'id': 'vm_to_delete',
                'startTime': '2019-01-01T00:00:00Z'
            }, {
                'id': 'vm_to_stay',
                'startTime': '2019-01-01T00:00:00Z'
            }]
        },
        # Second list_instance response
        {
            'instances': [{
                'id': 'vm_to_stay',
                'startTime': '2019-01-01T00:00:00Z'
            }]
        },
        # Third list_instance response
        {
            'instances': [{
                'id': 'vm_to_stay',
                'startTime': '2019-01-01T00:00:00Z'
            }, {
                'id': 'vm_new',
                'startTime': '2019-01-01T00:00:00Z'
            }]
        }
    ]