TDD vs. Unit testing

Question

My company is fairly new to unit testing our code. I've been reading about TDD and unit testing for some time and am convinced of their value. I've attempted to convince our team that TDD is worth the effort of learning and changing our mindsets on how we program but it is a struggle. Which brings me to my question(s).

There are many in the TDD community who are very religious about writing the test and then the code (and I'm with them), but for a team that is struggling with TDD does a compromise still bring added benefits?

I can probably succeed in getting the team to write unit tests once the code is written (perhaps as a requirement for checking in code) and my assumption is that there is still value in writing those unit tests.

What's the best way to bring a struggling team into TDD? And failing that is it still worth writing unit tests even if it is after the code is written?

EDIT

What I've taken away from this is that it is important for us to start unit testing, somewhere in the coding process. For those in the team who pickup the concept, start to move more towards TDD and testing first. Thanks for everyone's input.

FOLLOW UP

We recently started a new small project and a small portion of the team used TDD, the rest wrote unit tests after the code. After we wrapped up the coding portion of the project, those writing unit tests after the code were surprised to see the TDD coders already done and with more solid code. It was a good way to win over the skeptics. We still have a lot of growing pains ahead, but the battle of wills appears to be over. Thanks for everyone who offered advice!

Answer 1

It's imho better to have 50% test coverage with "code first, test after" and a 100% completed library, than 100% test coverage and a 50% completed library with TDD. After a while, your fellow developers will hopefully find it entertaining and educational to write tests for all of the public code they write, so TDD will sneak its way into their development routine.

Answer 2

It is absolutely still worth writing the unit tests after code is written. It's just that sometimes it's often harder because your code wasn't designed to be testable, and you may have overcomplicated it.

I think a good pragmatic way to bring a team into TDD is to provide the alternative method of "test-during development" in the transition period, or possibly in the long-term. They should be encouraged to TDD sections of code that seem natural to them. However, in sections of code that seem difficult to approach test-first or when using objects that are predetermined by a non-agile A&D process, developers can be given the option of writing a small section of the code, then writing tests to cover that code, and repeating this process. Writing unit tests for some code immediately after writing that code is better than not writing any unit tests at all.

Answer 3

If the team is floundering at implementing TDD, but they weren't creating any Unit Tests before...then start them off by creating Unit Tests after their code is written. Even Unit tests written after the code are better than no Unit Tests at all!

Once they're proficient at Unit Testing (and everything that comes with it), then you can work on getting them to create the tests first...and code second.

Answer 4

I just read this on a calendar: "Every rule, executed to its utmost, becomes ridiculous or even dangerous." So my suggestion is not to be religious about it. Every member of your team must find a balance between what they feel "right" when it comes to testing. This way, every member of your team will be most productive (instead of, say, thinking "why do I have to write this sti**** test??").

So some tests are better than none, tests after the code are better than few tests and testing before the code is better than after. But each step has its own merits and you shouldn't frown upon even small steps.

Answer 5

Well, if you do not write tests firsts it's not "Test Driven", it's just testing. It has benefits in itself and if you allready have a code base adding tests for it is certainly usefull even if it's not TDD but merely testing.

Writing tests first is about focusing on what the code should do before writing it. Yes you also get a test doing that and it's good, but some may argue it's not even the most important point.

What I would do is train the team on toy projects like these (see Coding Dojo, Katas) using TDD (if you can get experienced TDD programmers to participate in such workshop it would be even better). When they'll see the benefits they will use TDD for the real project. But meanwhile do not force them, it they do not see the benefit they won't do it right.

Answer 6

If they're new to testing than IMO start off testing code that's already been written and slowly graduate to writing tests first. As someone trying to learn TDD and new to unit testing, I've found it kind of hard to do a complete 180 and change my mindset to write tests before code, so the approach I'm taking is sort of a 50-50 mix; when I know exactly what the code will look like, I'll write the code and then write a test to verify it. For situations where I'm not entirely sure then I'll start with a test and work my way backwards.

Also remember that there is nothing wrong with writing tests to verify code, instead of writing code to satisfy tests. If your team doesn't want to go the TDD route then don't force it on them.

Answer 7

TDD is about design! So if you use it, you will be sure to have a testable design of your code, making it easier to write your tests. If you write tests after the code is written they are still valuable but IMHO you will be wasting time since you will probably not have a testable design.

One suggestion I can give to you to try to convince your team to adopt TDD is using some of the techniques described on Mary Linn and Linda Rising book : Patterns for Introducing new Ideas

Answer 8

Starting to build JUnit test classes is the way to start, for existing code it's the only way to start. In my experience it is very usefull to create test classes for existing code. If management thinks this will invest too much time, you can propose to only write test classes when the corresponding class is found to contain a bug, or is in need of cleanup.

For the maintenance process the approach to get the team over the line would be to write JUnit tests to reproduce bugs before you fix them, i.e.

• bug is reported
• create JUnit test class if needed
• add a test that reproduces the bug
• fix your code
• run the test to show the current code does not reproduce the bug

You can explain that by "documenting" bugs in this way will prevent those bugs from creeping back in later. That is a benefit the team can experience immediately.

Answer 9

One of the most useful aspect of unit testing is ensuring the continuing correctness of already working code. When you can refactor at will, let an IDE remind you of compile time errors, and then click a button to let your tests spot any potential runtime errors--sometimes arriving in previously trivial blocks of code, then I think you will find your team starting to appreciate TDD. So starting with testing existing code is definitely useful.

Also, to be blunt, I have learned more about how to write testable code by trying to test written code than from starting with TDD. It can be too abstract at first if you are trying to think of contracts that will both accomplish the end goal and allow testing. But when you look at code and can say "This singleton here completely spoils dependency injection and makes testing this impossible," you start to develop an appreciation for what patterns make your testing life easier.

Answer 10

This is something that your team will have to have its own successes with before they begin to believe it in. I'll rant about my nUnit epiphany for anyone who cares:

About 5 years ago I discovered nUnit when working on a project. We had almost completed V1.0 and I created a few tests just to try out this new tool. We had a lot of bugs (obviously!) because we were a new team, on a tight deadline, high expectations (sound familiar?) etc. Anyway we got 1.0 in and started on 1.1. We re-orged the team a little bit and I got 2 devs assigned to me. I did a 1-hour demo for them and told them that everything we wrote had to have a test case with it. We constantly ran "behind" the rest of the team during the 1.1 dev cycle because we were writing more code, the unit tests. We ended up working more but here's the payoff -- when we finally got into testing we had exactly 0 bugs in our code. We helped everyone else debug and repair their bugs. In the postmortem, when the bug counts showed up, it got EVERYONE's attention.

I'm not dumb enough to think you can test your way to success but I am a true believer when it comes to unit tests. The project adopted nUnit and it soon spread to the company for all .Net projects as a result of 1 success. Total time period for our V1.1 release was 9 dev weeks so it was definitely NOT an overnight success. But long term, it proved successful for our project and the company we built solutions for.

Answer 11

There is no doubt that testing (First, While or even After) will save your bacon, and improve your productivity and confidence. I recommend adopting it!

I was in a similar situation, because I was a "noob" developer, I was often frustrated when working on team project by the fact that a contribution had broken the build. I did not know if I was to blame or even in some cases, who to blame. But I was more concerned that I was doing to same thing to my fellow developers. This realisation then motivated to adopt some TDD strategies. Our team started have silly games, and rules, like you cannot go home till all your tests pass, or if you submit something without a test, then you have to buy everyone "beer/lunch/etc" and it made TDD more fun.

Answer 12

TDD is a tool that developers can use to produce better code. I happen to feel that the exercise of writing testable code is as least as valuable as the tests themselves. Isolating the IUT (Implementation Under Test) for testing purposes has the side affect of decoupling your code.

TDD isn't for everyone, and there's no magic that will get a team to choose to do it. The risk is that unit test writers that don't know what's worth testing will write a lot of low value tests, which will be cannon fodder for the TDD skeptics in your organization.

I usually make automated Acceptance Tests non-negotiable, but allow developers to adopt TDD as it suits them. I have my experienced TDDers train/mentor the rest and "prove" the usefulness by example over a period of many months.

This is as much a social/cultural change as it is a technical one.

Answer 13

I have done this in many organizations and I have found the single best way to get TDD started and followed is to set up pair programming. If you have someone else you can count on that knows TDD then the two of you can split up and pair with other developers to actually do some paired programming using TDD. If not I would train someone who will help you to do this before presenting it to the rest of the team.

One of the major hurdles with unit testing and especially TDD is that developers don't know how to do it, so they can not see how it can be worth their time. Also when you first start out, it is much slower and doesn't seem to provide benefits. It is only really providing you benefits when you are good at it. By setting up paired programming sessions you can quickly get developers to be able to learn it quickly and get good at it quicker. Additionally they will be able to see immediate benefits from it as you work though it together.

This approach has worked many times for me in the past.

Answer 14

I can probably succeed in getting the team to write unit tests once the code is written (perhaps as a requirement for checking in code) and my assumption is that there is still value in writing those unit tests.

There is absolutely no doubt about the fact that there is value in unit tested code (regardless of when tests were written) and I include "the code is unit tested" in the "Definition of Done". People may use TDD or not, as long as they test.

Regarding version control, I like to use "development branches" with a unit tested policy (i.e. the code compiles and builds, all unit tests pass). When features are done, they are published from development branches to the trunk. In other words, the trunk branch is the "Done branch" (No junk on the trunk!) and has a shippable policy (can release at any time) which is more strict and includes more things than "unit tested".

Answer 15

One powerful way to discover the benefits of TDD is to do a significant rewrite of some existing functionality, perhaps for performance reasons. By creating a suite of tests that do a good job covering all the functionality of the existing code, this then gives you the confidence to refactor to your heart's content with full confidence that your changes are safe.

Note that in this case I'm talking about testing the design or contract - unit tests that test implementation details will not be suitable here. But then again, TDD can't test implementation by definition, as they are supposed to be written before the implementation.

Answer 16

If you have design sessions before writing code or have to produce a design doc, then you could add Unit Tests as the tangible outcome of a session.

This could then serve as a specification as to how your code should work. Encourage pairing on the design session, to get people talking about how something should work and what it should do in given scenarios. What are the edge cases, with explicit test cases for them so everyone knows what it's going to do if given a null argument for example.

An aside but BDD also may be of interest

Answer 17

You may find some traction by showing an example or two where TDD results in less code being written - because you only write code required to make the test pass, the temptation to gold-plate or engage in YAGNI is easier to resist. Code you don't write doesn't need to be maintained, refactored, etc, so it's a "real savings" that can help sell the concept of TDD.

If you can clearly demonstrate the value in terms of time, cost, code and bugs saved, you may find it's an easier sell.