How much testing should we do ?

There are question people asked that can you test the software fully? Can you test everything ?then quick response  of some people that -"yes", Everything should be tested. But is it possible to test everything (All combination of inputs and conditions)?

As Tester we need to give confidence to the software/product, The software is good to be  release whether you test completely or you do exhausting testing but it’s very important what customer and project manager expecting from you what they ask for.

when we say how much testing is enough we need to take care of level of risk in product/project then that risk can be business risk, technical risk etc. we need to consider time and budget. That mean in what time we need to complete our testing activity by given budget.

Now the question come over here can we test everything ?Suppose we need to test one text box field which can take only a character,so here can you going to check all upper and lower character ,special character for valid values and for invalid values are you going to check all digits and blank space. Here we are talking about only one text box but when more than one text box will come so can you imagine how much combination and inputs require, does it possible to test everything in give time ? No, it's not possible .In that case you need to do testing with smart way using various type of technique ,understanding the customer requirements, risk and of course you need to do all those thing  by given time frame.