This question already has an answer here: Why can\'t the IT industry deliver lar

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This question already has an answer here:
Why can't the IT industry deliver large, faultless projects quickly as in other industries? 29 answers
We are developing an application that goes through many testers before reaching our client.

Finally, when it reaches the client, they find some more bugs and report to us, and this has become a tedious process. There are some bugs which I personally can't fix, because it requires me to modify most of the inner code, and I am not even sure that it might work.

Questions:

Why do bugs get reported even after going through so much testing? Is it our requirements' issue?

Our client doesn't seem happy for anything we provide. Are we doing something incorrect?

Has anyone developed any application that were totally bug free? What is the process? Why can't we deploy the application with minor bugs? Are we supposed to be perfectionist?

Is the current scenario the correct process of development and testing? If not, what is an efficient way where developers, testers and client get the maximum benefit together?

Explanation / Answer

The closest you get to a bug-free application, the more expensive it gets. It's like targeting 100% code coverage: you spend the same amount of time and money getting from 0% to 95%, from 95% to 99% and from 99% to 99.9%.

Do you need this extra 0.1% of code coverage or quality? Probably yes, if you're working on a software product which controls the cooling system of a nuclear reactor. Probably not if you're working on a business application.

Also, making high quality software requires a very different approach. You can't just ask a team of developers who spent their life writing business apps to create a nearly bug-free application. High quality software requires different techniques, such as formal proof, something you certainly don't want to use in a business app, because of the extremely high cost it represents.

As I explained in one of my articles:

Business apps shouldn't target the quality required for life-critical software, because if those business apps fail from time to time, it just doesn't matter. I've seen bugs and downtime in websites of probably every large corporation, Amazon being the only exception. This downtime and those bugs are annoying and maybe cost the company a few thousands of dollars per month, but fixing it would be much more expensive.

Cost should be the primary focus, and should be studied pragmatically. Let's imagine a bug which is affecting 5 000 customers and is so important that those customers will leave forever. Is this important? Yes? Think more. What if I say that each of those customers is paying $10 per year and that it will cost almost $100 000 to fix the bug? Bug fixing now looks much less interesting.

Now to answer your questions specifically:

why do bugs get reported even after going through so much testing? Is it our requirements issue? Our client doesn't seem happy for anything we provide? are we doing something incorrect?

Lots of things can go wrong. By testing, do you mean actual automated testing? If not, this is a huge problem on itself. Do testers understand the requirements? Do you communicate with the customer on regular basis

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