On my '90 Corolla, the power steering works. A belt has begun squealing, especially when I turn a hard right. I loosened the power steering belt a little and it squeals less. The steering is stiffer, but still comfortable. So I'm wondering if the power steering pump is going bad. The power steering fluid reservoir has the correct fluid level. Is there an objective way to test the condition of a power steering pump? Can I tell anything by removing the belt and turning the pump's pulley by hand while the engine is shut off?