Can unit testing be successfully added into an existing production project? If so, how and is it worth it?

Question

I\'m strongly considering adding unit testing to an existing project that is in production. It was started 18 months ago before I could really see any benefit of TDD

Answer 1

Yes it can: Just try to make sure all code you write from now has a test in place.

If the code that is already in place needs to be modified and can be tested, then do so, but it is better not to be too vigorous in trying to get tests in place for stable code. That sort of thing tends to have a knock-on effect and can spiral out of control.

Answer 2

Is it worth the effort for an existing solution that's in production?

Yes. But you don't have to write all unit tests to get started. Just add them one by one.

Would it better to ignore the testing for this project and add it in a possible future re-write?

No. First time you are adding code which breaks the functionality, you will regret it.

What will be more benefical; spending a few weeks adding tests or a few weeks adding functionality?

For new functionality (code) it is simple. You write the unit test first and then the functionality. For old code you decide on the way. You don't have to have all unit tests in place... Add the ones that hurt you most not having... Time (and errors) will tell on which one you have to focus ;)

Answer 3

There is so many good answers so I will not repeat their content. I checked your profile and it seems you are C# .NET developer. Because of that I'm adding reference to Microsoft PEX and Moles project which can help you with autogenerating unit tests for legacy code. I know that autogeneration is not the best way but at least it is the way to start. Check this very interesting article from MSDN magazine about using PEX for legacy code.

Answer 4

Yes. No. Adding tests.

Going towards a more TDD approach will actually better inform your efforts to add new functionality and make regression testing much easier. Check it out!

Answer 5

• Is it worth the effort for an existing solution that's in production?

Yes!

• Would it better to ignore the testing for this project and add it in a possible future re-write?

No!

• What will be more benefical; spending a few weeks adding tests or a few weeks adding functionality?

Adding testing (especially automated testing) makes it much easier to keep the project working in the future, and it makes it significantly less likely that you'll ship stupid problems to the user.

Tests to put in a priori are ones that check whether what you believe the public interface to your code (and each module in it) is working the way you think. If you can, try to also induce each isolated failure mode that your code modules should have (note that this can be non-trivial, and you should be careful to not check too carefully how things fail, e.g., you don't really want to do things like counting the number of log messages produced on failure, since verifying that it is logged at all is enough).

Then put in a test for each current bug in your bug database that induces exactly the bug and which will pass when the bug is fixed. Then fix those bugs! :-)

It does cost time up front to add tests, but you get paid back many times over at the back end as your code ends up being of much higher quality. That matters enormously when you're trying to ship a new version or carry out maintenance.

Answer 6

I would like to start this answer by saying that unit testing is really important because it will help you arrest bugs before they creep into production.

Identify the areas projects/modules where bugs have been re-introduced. start with those projects to write tests. It perfectly makes sense to write tests for new functionality and for bug fix.

Is it worth the effort for an existing solution that's in production?

Yes. You will see the effect of bugs coming down and maintenance becoming easier

Would it better to ignore the testing for this project and add it in a possible future re-write?

I would recommend to start if from now.

What will be more benefical; spending a few weeks adding tests or a few weeks adding functionality?

You are asking the wrong question. Definitely, functionality is more important than anything else. But, rather you should ask if spending a few weeks adding test will make my system more stable. Will this help my end user? Will it help a new developer in the team to understand the project and also to ensure that he/she, doesn't introduce a bug due to lack of understanding of the overall impact of a change.