What is the point of Unit Testing

I have been looking at the unit testin开发者_运维问答g topic and honestly I have never yet seen it in a live application.

Im a little foggy on the subject.... A simple example is if I am populating a listbox with data, I would know through debugging if the data is being populated and if it wasnt it would probably be easy to figure out why. Futhermore I couldnt possibly put it in production if it wasnt work so, why would I need to do a unit test? I dont see the point of it.

What if you were working on an entirely different area of the site, but because of the way your code was constructed, the changes you made broke the code that fills the listbox with data? How long would it take you to discover that? Worse, what if it was someone else on the team who made such a change; someone who had no idea how the listbox-filling code worked at all? Or even someone who didn't know there was code to fill listboxes?

Unit testing gives you a set of tests that ensure you never regress and introduce bugs in areas of your program that have already been proven to work, because you run the unit tests after every change and refactoring. Unit testing lets you program without fear.

Furthermore, by designing your code to be testable, you necessarily create a loosely-coupled architecture that follows a large list of best practices, e.g. dependency injection.

The point is that by using unit tests you are sure that each class is working as intended.

What is the value of that, apart from knowing that it works under certain conditions?

When you refactor your code, change the design, rework a (supposedly) unrelated piece of code, if your tests still run correctly you know your have not broken any functionality.

Unit testing is both about ensuring that the code you write conforms to your expectations and that any changes to it still conform to them.

There're many pros and cons with using Testing. Take a look at Art Of Unit Testing somehow, this book greatly covers subjects of unit testing. Also, you can find out why you should do unit testing.

In your example, imagine you had to check populating of listbox, combobox and other data at about on 15 web pages. How much browser reload, mouse clicks, breakpoint hits and runs should you have to make to test it with debug? Many. But with unit testing, one of the core rules is that tests should be run simply, by single click. If you design unit tests correctly, you can test thousands and thousands of code with the single click

Unit testing will give you an opportunity to test your logic without hitting the sql server and firing Cassini or IIS Express. (Of course you need to implement dependency injection firstly on your main project and mock them on your test application)

Think about you have written hundreds of test methods. And you will run all the test methods in bulk. This could take a minutes and more depending on your data structure. Buy if you implement dependency injection on your project and mock them in your test, this will take quite a small time.

here is a source which you could find a good article on dependency injection : http://haacked.com/archive/2007/12/07/tdd-and-dependency-injection-with-asp.net-mvc.aspx

this my reason of using unit testing. if your project is really big enough, I think your should also consider Test-driven development (TDD)