What's the best argument to convince developers to learn TDD?

Question

Let me first come out of closet. I'm a TDD believer. I'm trying to practice Test Driven Development as much as I can.

Some developers at my work refuse to even try it. I myself started TDD by trying to prove to one of my peers that Test Driven Development is a bad idea. The arguments are:

• Why? I was pretty successful developer so far.
• It's going to slow me down.

What's the best pro TDD argument did hear or used?

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See also: What is the best reason for unit testing?

Answer 1

Perhaps they know better.

Unit testing by developers is an extremely useful practice and I cannot overemphasize its benefits, not only during initial development but also during refactoring when unit tests can catch early not only ordinary code defects but also the break of assumptions made by developers that were never captured in formal documentation and thus are likely lost by the time refactoring occurs.

That being said, TDD is no magic pixie dust:

1. the 'just write enough code to pass the test' approach gives false positives. There are often known fallacies and problems that the 'just enough' approach fails to address. Quick examples that come to mind are distributed systems fallacies or NUMA performance problems. Just capturing those requirements into simply expressing those test cases for TDD would turn into a full time job in itself.
2. the explosion of moqs goes out of control for any serious size project. mocks are code like any other code, they need to be maintained and just don't write themselves out of the blue.
3. TDD is often used as an excuse to eliminate QA testing. 'our developer have already written tested id, lets ship it' neglects completely the end-to-end feature oriented testing QA should cover
4. I don't trust the fox guarding the hen house. A wrong algorithm can still pass TDD with flying colors if the same mistakes are made in both the test and in the implementation.
5. All methodologies in the end try to use process to substitute talent.

My main quarrel with TDD is that is presented as a magic solution to most development problems but its cost is kept under the table by its advocates. Doubling or tripling your code base with moqs does not come for free. I much rather see a few comprehensive unit tests written during development. The test-first TDD approach, I'm yet to see its benefits in a real size project.

I understand I'll be egg-ed to death now for posting this, but what the heck, who cares...