What are some reasons why a sole developer should use TDD?

Question

I'm a contract programmer with lots of experience. I'm used to being hired by a client to go in and do a software project of one form or another on my own, usually from nothing. That means a clean slate, almost every time. I can bring in libraries I've developed to get a quick start, but they're always optional. (and depend on getting the right IP clauses in the contract) Many times I can specify or even design the hardware platform... so we're talking serious freedom here.

I can see uses for constructing automated tests for certain code: Libraries with more than trivial functionality, core functionality with a high number of references, etc. Basically, as the value of a piece of code goes up through heavy use, I can see it would be more and more valuable to automatically test that code so that I know I don't break it.

However, in my situation, I find it hard to rationalize anything more than that. I'll adopt things as they prove useful, but I'm not about to blindly follow anything.

I find many of the things I do in 'maintenance' are actually small design changes. In this case, the tests would not have saved me anything and now they'd have to change too. A highly iterative, stub-first design approach works very well for me. I can't see actually saving myself that much time with more extensive tests.

Hobby projects are even harder to justify... they're usually anything from weekenders up to a say month long. Edge-case bugs rarely matter, it's all about playing with something.

Reading questions such as this one, The most voted on response seems to say that in that poster's experience/opinion TDD actually wastes time if you've got less than 5 people (even assuming a certain level of competence/experience with TDD). However, that appears to be covering initial development time, not maintenance. It's not clear how TDD stacks up over the entire life cycle of a project.

I think TDD could be a good step in the worthwhile goal of improving the quality of the products of our industry as a whole. Idealism on it's own is no longer all that effective at motivating me, though.

I do think TDD would be a good approach in large teams, or any size team containing at least one unreliable programmer. That's not my question.

Why would a sole developer with a good track record adopt TDD?

I'd love to hear of any kind of metrics done (formally or not) on TDD... focusing on solo developers or very small teams.

Failing that, anecdotes of your personal experiences would be nice, too. :)

Please avoid stating opinion without experience to back it. Let's not make this an ideology war. Also the skip greater employment options argument. This is simply an efficiency question.

Answer 1

I find it even more useful when flying solo. With nobody around to bounce ideas off of and nobody around to perform peer reviews, you will need some assurance that you're code is solid. TDD/BDD will provide that assurance for you. TDD is a bit contraversial, though. Others may completely disagree with what I'm saying.

EDIT: Might I add that if done right, you can actually generate specifications for your software at the same time you write tests. This is a great side effect of BDD. You can make yourself look like super developer if you're cranking out solid code along with specs, all on your own.

Answer 2

It does not matter whether you are the sole developer or not. You have to think of it from the application point of view. All the applications needs to work properly, all the applications need to be maintained, all the applications needs to be less buggy. There are of course certain scenarios where a TDD approach might not suit you. This is when the deadline is approaching very fast and no time to perform unit testing.

Anyways, TDD does not depend on a solo or a team environment. It depends on the application as a whole.

Answer 3

I don't have an enormous amount of experience, but I have had the experience of seeing sharply-contrasted approaches to testing.

In one job, there was no automated testing. "Testing" consisted of poking around in the application, trying whatever popped in your head, to see if it broke. Needless to say, it was easy for flat-out-broken code to reach our production server.

In my current job, there is lots of automated testing, and a full CI-system. Now when code gets broken, it is immediately obvious. Not only that, but as I work, the tests really document what features are working in my code, and what haven't yet. It gives me great confidence to be able to add new features, knowing that if I break existing ones, it won't go unnoticed.

So, to me, it depends not so much on the size of the team, but the size of the application. Can you keep track of every part of the application? Every requirement? Every test you need to run to make sure the application is working? What does it even mean to say that the application is "working", if you don't have tests to prove it?

Just my $0.02.

Answer 4

I'm going to answer this question quite quickly, and hopefully you will start to see some of the reasoning, even if you still disagree. :)

If you are lucky enough to be on a long-running project, then there will be times when you want to, for example, write your data tier first, then maybe the business tier, before moving on up the stack. If your client then makes a requirement change that requires re-work on your data layer, a set of unit tests on the data layer will ensure that your methods don't fail in undesirable ways (assuming you update the tests to reflect the new requirements). However, you are likely to be calling the data layer method from the business layer as well, and possibly in several places.

Let's assume you have 3 calls to a method in the business layer, but you only modify 2. In the third method, you may still be getting data back from your data layer that appears to be valid, but may break some of the assumptions you coded months before. Unit tests at this level (and above) should have been designed to spot broken assumptions, and in failing they should highlight to you that there is a section of code that needs to be revisited.

I'm hoping that this very simplistic example will be enough to get you thinking about TDD a little more, and that it might create a spark that makes you consider using it. Of course, if you still don't see the point, and you are confident in your own abilities to keep track of many thousands of lines of code, then I have no place to tell you you should start TDD.

Answer 5

I'm not about to blindly follow anything.

That's the right attitude. I use TDD all the time, but I don't adhere to it as strictly as some.

The best argument (in my mind) in favor of TDD is that you get a set of tests you can run when you finally get to the refactoring and maintenance phases of your project. If this is your only reason for using TDD, then you can write the tests any time you want, instead of blindly following the methodology.

The other reason I use TDD is that writing tests gets me thinking about my API up front. I'm forced to think about how I'm going to use a class before I write it. Getting my head into the project at this high level works for me. There are other ways to do this, and if you've found other methods (there are plenty) to do the same thing, then I'd say keep doing what works for you.

Answer 6

TDD is not about testing it's about writing code. As such, it provides a lot of benefits to even a single developer. For many developers it is a mindshift to write more robust code. For example, how often do you think "Now how can this code fail?" after writing code without TDD? For many developers, the answer to that question is none. For TDD practioners it shifts the mindset to to doing things like checking if objects or strings are null before doing something with them because you are writing tests to specifically do that (break the code).

Another major reason is change. Anytime you deal with a customer, they can never seem to make up their minds. The only constant is change. TDD helps as a "safety net" to find all the other areas that could break.Even on small projects this can keep you from burning up precious time in the debugger.

I could go and on, but I think saying that TDD is more about writing code than anything should be enough to justify it's use as a sole developer.

Answer 7

The point about writing the tests first is that it enforces the requirements and design decisions you are making. When I mod the code, I want to make sure those are still enforced and it is easy enough to "break" something without getting a compiler or run-time error.

I have a test-first approach because I want to have a high degree of confidence in my code. Granted, the tests need to be good tests or they don't enforce anything.

I've got some pretty large code bases that I work on and there is a lot of non-trivial stuff going on. It is easy enough to make changes that ripple and suddenly X happens when X should never happen. My tests have saved me on several occasions from making a critical (but subtle) error that might have gone unnoticed by human testers.

When the tests do fail, they are opportunities to look at them and the production code and make sure that it is correct. Sometimes the design changes and the tests will need to be modified. Sometimes I'll write something that passes 99 out of 100 tests. That 1 test that didn't pass is like a co-worker reviewing my code (in a sense) to make sure I'm still building what I'm supposed to be building.

Answer 8

I tend to agree with the validity of your point about the overhead of TDD for 'one developer' or 'hobby' projects not justifying the expenses.

You have to consider however that most best practices are relevant and useful if they are consistently applied for a long period of time.

For example TDD is saving you testing/bugfixing time in a long run, not within 5 minutes after you've created the first unit test.

You're a contract programmer which means that you will leave your current project when it will be finished and will switch to something else, most likely in another company. Your current client will have to maintain and support your application. If you do not leave the support team a good framework to work with they will be stuck. TDD will help the project to be sustainable. It will increase the stability of the code base so other people with less experience will not be able not do too much damage trying to change it.

The same applies for the hobby projects. You may be tired of it and will want to pass it to someone. You might become commercially successful (think Craiglist) and will have 5 more people working besides you.

Investment in proper process always pays-off, even if it is just gained experience. But most of the time you will be grateful that when you started a new project you decided to do it properly

You have to consider OTHER people when doing something. You you have to think ahead, plan for growth, plan for sustainability.

If you don't want to do that - stick to the cowboy coding, it's much simpler this way.

P.S. The same thing applies to other practices:

• If you don't comment your code and you have ideal memory you'll be fine but someone else reading your code will not.
• If you don't document your discussions with the customer somebody else will not know anything about a crucial decision you made

etc ad infinitum

Answer 9

Tests allow you to refactor with confidence that you are not breaking the system. Writing the tests first allows the tests to define what is working behavior for the system. Any behavior that isn't defined by the test is by definition a by-product and allowed to change when refactoring. Writing tests first also drive the design in good directions. To support testability you find that you need to decouple classes, use interfaces, and follow good pattern (Inversion of Control, for instance) to make your code easily testable. If you write tests afterwards, you can't be sure that you've covered all the behavior expected of your system in the tests. You also find that some things are hard to test because of the design -- since it was likely developed without testing in mind -- and are tempted to skimp on or omit tests.

I generally work solo and mostly do TDD -- the cases where I don't are simply where I fail to live up to my practices or haven't yet found a good way that works for me to do TDD, for example with web interfaces.

Answer 10

I no longer refactor anything without a reasonable set of unit tests.

I don't do full-on TDD with unit tests first and code second. I do CALTAL -- Code A LIttle, Test A Little -- development. Generally, code goes first, but not always.

When I find that I've got to refactor, I make sure I've got enough tests and then I hack away at the structure with complete confidence that I don't have to keep the entire old-architecture-becomes-new-architecture plan in my head. I just have to get the tests to pass again.

I refactor the important bits. Get the existing suite of tests to pass.

Then I realize I forgot something, and I'm back to CALTAL development on the new stuff.

Then I see things I forgot to delete -- but are they really unused everywhere? Delete 'em and see what fails in the testing.

Just yesterday -- part way through a big refactoring -- I realized that I still didn't have the exact right design. But the tests still had to pass, so I was free to refactor my refactoring before I was even done with the first refactoring. (whew!) And it all worked nicely because I had a set of tests to validate the changes against.

For flying solo TDD is my copilot.

Answer 11

I feel that as a solo developer on a project, especially a larger one, you tend to be spread pretty thin.
You are in the middle of a large refactoring when all of a sudden a couple of critical bugs are detected that for some reason did not show up during pre-release testing. In this case you have to drop everything and fix them and after having spent two weeks tearing your hair out you can finally get back to whatever you were doing before.
A week later one of your largest customers realizes that they absolutely must have this cool new shiny feature or otherwise they won't place the order for those 1M units they should have already ordered a month ago.
Now, three months later you don't even remember why you started refactoring in the first place let alone what the code you are refactoring was supposed to do. Thank god you did a good job writing those unit tests because at least they tell you that your refactored code is still doing what it was supposed to do.
Lather, rinse, repeat.

..story of my life for the past 6 months. :-/

Answer 12

Sole developer should use TDD on his project (track record does not matter), since eventually this project could be passed to some other developer. Or more developers could be brought in.

New people will have extremely have hard time working with the code without the tests. They will break things.

Answer 13

Does your client own the source code when you deliver the product? If you can convince them that delivering the product with unit tests adds value, then you are up-selling your services and delivering a better product. From the client's perspective, test coverage not only ensures quality, it allows future maintainers to understand the code much more readily since the tests isolate functionality from the UI.

Answer 14

My best experience with TDD is centered around the pyftpdlib project. Most of the development is done by the original author, and I've made a few small contributions, but it's essentially a solo project. The test suite for the project is very thorough, and tests all the major features of the FTPd library. Before checking in changes or releasing a version, all tests are checked, and when a new feature is added, the test suite is always updated as well.

As a result of this approach, this is the only project I've ever worked on that didn't have showstopper bugs appear after a new release, have changes checked in that broke a major feature, etc. The code is very solid and I've been consistently impressed with how few bug reports have been opened during the life of the project. I (and the original author) attribute much of this success to the comprehensive test suite and the ability to test every major code path at will.

From a logical perspective, any code you write has to be tested, and without TDD then you'll be testing it yourself manually. On the flip side to pyftpdlib, the worst code by number of bugs and frequency of major issues, is code that is/was solely being tested by the developers and QA trying out new features manually. Things don't get tested because of time crunch or falling through the cracks. Old code paths are forgotten and even the oldest stable features end up breaking, major releases end up with important features non-functional. etc. Manual testing is critically important for verification and some randomization of testing, but based on my experiences I'd say that it's essential to have both manual testing and a carefully constructed unit test framework. Between the two approaches the gaps in coverage are smaller, and your likelihood of problems can only be reduced.

Answer 15

I think TDD as a methodology is not just about "having tests when making changes", thus it does not depend on team- nor on project size. It's about noting one's expectations about what a pice of code/an application does BEFORE one starts to really think about HOW the noted behaviour is implemented. The main focus of TDD is not only having test in place for written code but writing less code because you just do what make the test green (and refactor later).

If you're like me and find it quite hard to think about what a part/the whole application does WITHOUT thinking about how to implement it, I think its fine to write your test after your code and thus letting the code "drive" the tests.

If your question isn't so much about test-first (TDD) or test-after (good coding?) I think testing should be standard practise for any developer, wether alone or in a big team, who creates code which stays in production longer than three months. In my expirience that's the time-span after which even the original author has to think hard about what these twenty lines of complex, super-optimized, but sparsely documented code really code do. If you've got tests (which cover all paths throughth the code), there less to think - and less to ERR about, even years later...

Answer 16

Here are a few memes and my responses:

"TDD made me think about how it would fail, which made me a better programmer"

Given enough experience, being higly concerned with failure modes should naturally become part of your process anyway.

"Applications need to work properly"

This assumes you are able to test absolutely everything. You're not going to be any better at covering all possible tests correctly than you were at writing the functional code correctly in the first place. "Applications need to work better" is a much better argument. I agree with that, but it's idealistic and not quite tangible enough to motivate as much as I wish it would. Metrics/anecdotes would be great here.

"Worked great for my <library component X>"

I said in the question I saw value in these cases, but thanks for the anecdote.

"Think of the next developer"

This is probably one of the best arguments to me. However, it is quite likely that the next developer wouldn't practice TDD either, and it would therefore be a waste or possibly even a burden in that case. Back-door evangelism is what it amounts to there. I'm quite sure a TDD developer would really appeciate it, though.

How much are you going to appreciate projects done in deprecated must-do methodologies when you inherit one? RUP, anyone? Think of what TDD means to next developer if TDD isn't as great as everyone thinks it is.

"Refactoring is a lot easier"

Refactoring is a skill like any other, and iterative development certainly requires this skill. I tend to throw away considerable amounts of code if I think the new design will save time in the long run, and it feels like there would be an awful number of tests thrown away too. Which is more efficient? I don't know.

...

I would probably recommend some level of TDD to anyone new... but I'm still having trouble with the benefits for anyone who's been around the block a few times already. I will probably start adding automated tests to libraries. It's possible that after doing that, I'll see more value in doing it generally.

Answer 17

I'm also a contract programmer. Here are my 12 Reasons Why I Love Unit Tests.

Answer 18

Ok my turn... I'd do TDD even on my own (for non-spike/experimental/prototype code) because

• Think before you leap: forces me to think what I want to get done before i start cranking out code. What am I trying to accomplish here.. 'If I assume I already had this piece.. how would I expect it to work?' Encourages interface-in design of objects.
• Easier to change: I can make modifications with confidence.. 'I didn't break anything in step1-10 when i changed step5.' Regression testing is instantaneous
• Better designs emerge: I've found better designs emerging without me investing effort in a design activity. test-first + Refactoring lead to loosely coupled, minimal classes with minimal methods.. no overengineering.. no YAGNI code. The classes have better public interfaces, small methods and are more readable. This is kind of a zen thing.. you only notice you got it when you 'get it'.
• The debugger is not my crutch anymore : I know what my program does.. without having to spend hours stepping thru my own code. Nowadays If I spend more than 10 mins with the debugger.. mental alarms start ringing.
• Helps me go home on time I have noticed a marked decrease in the number of bugs in my code since TDD.. even if the assert is like a Console trace and not a xUnit type AT.
• Productivity / Flow: it helps me to identify the next discrete baby-step that will take me towards done... keeps the snowball rolling. TDD helps me get into a rhythm (or what XPers call flow) quicker. I get a bigger chunk of quality work done per unit time than before. The red-green-refactor cycle turns into... a kind of perpetual motion machine.
• I can prove that my code works at the touch of a button
• Practice makes perfect I find myself learning & spotting dragons faster.. with more TDD time under my belt. Maybe dissonance.. but I feel that TDD has made me a better programmer even when I don't go test first. Spotting refactoring opportunities has become second nature...

I'll update if I think of any more.. this is what i came up with in the last 2 mins of reflection.

Answer 19

TDD lets me more clearly define the problem in my head. That helps me focus on implementing just the functionality that is required, and nothing more. It also helps me create a better API, because I'm writing a "client" before I write the code itself. I can also refactor without having to worry about breaking anything.

Answer 20

Motivated self interest.

In my case, sole developer translates to small business owner. I've written a reasonable amount of library code to (ostensibly) make my life easier. A lot of these routines and classes aren't rocket science, so I can be pretty sure they work properly (at least in most cases) by reviewing the code, some some spot testing and debugging into the methods to make sure they behave the way I think they do. Brute force, if you will. Life is good.

Over time, this library grows and gets used in more projects for different customers. Testing gets more time consuming. Especially cases where I'm (hopefully) fixing bugs and (even more hopefully) not breaking something else. And this isn't just for bugs in my code. I have to be careful adding functionality (customers keep asking for more "stuff") or making sure code still works when moved to a new version of my compiler (Delphi!), third party code, runtime environment or operating system.

Taken to the extreme, I could spend more time reviewing old code than working on new (read: billable) projects. Think of it as the angle of repose of software (how high can you stack untested software before it falls over :).

Techniques like TDD gives me methods and classes that are more thoughtfully designed, more thoroughly tested (before the customer gets them) and need less maintenance going forward.

Ultimately, it translates to less time doing maintenance and more time to spend doing things that are more profitable, more interesting (almost anything) and more important (like family).