Why automobile manufacturer are recalling their cars?

Hi, i am a enthusiast of automobile and after searching a lot of options on net for discussion i finally came on this forum which is quite different as compare to other forums. So, i was figuring to discuss this query which came into my mind was that why automobile manufacturer's are recalling their car.

My question is when they manufacture the car they didn't test it before selling it. What is the actual problem?

Any company will never launch their products unless and until they test it. But after launching if there are some problems which are registered in high amount then company recalls, so that they didn't loose their customer trust.