You are trying to mock already mocked class. See if you have registered your service somewhere as a facade - Laravel has a lot of auto generated defaults, which is hard to notice. Here is a facades shouldReceive method:
public static function shouldReceive()
{
$name = static::getFacadeAccessor();
if (static::isMock())
{
$mock = static::$resolvedInstance[$name];
}
else
{
$mock = static::createFreshMockInstance($name);
}
return call_user_func_array(array($mock, 'shouldReceive'), func_get_args());
}