In my experience – and I can only speak from my experience – the answer for me is:   “yes, but it’s not a religion.”   On the one hand, there is always the (legitimate) urge to “get started.”   On the other, there is the (also legitimate) concern that it takes exactly the same amount of time to write source-code that you won’t use, as it does to write source-code that you will.

A very interesting viewpoint on this picture was described in a book, Managing the Mechanism, which so far as I know is available right now only on the Kindle.   The premise is that, when you are writing software, you are constructing a machine ... and, not just “a machine,” but “an automaton.”   A mechanical machine that has to successfully play Chess and win.   When you frame the challenge of software in that way, the importance of specification and testing becomes much more intuitive.

I don’t reach for textbooks to tell me what to do.   When faced with a task of any significant complexity, I definitely do find a test-driven approach to be beneficial.   Why?   Because I know the value of actually being able to use myModule; with the same degree of confidence (and the same technical justification for holding such confidence ...) as I know that I am able to do when I use DBI;.

When you use a battle-tested CPAN module such as this one, you do not give a second thought as to whether this module will actually perform as the perldoc promises you that it will.   And, if you have ever paid attention while that module and its many brethren are being installed, you will know why this is so.   You will recognize the need to be able to make the same statements and to have the same assurances with regard to “the stuff that you wrote.”

So ... “it’s not a religion, but it is a Best Practice that can be routinely achieved.”   With a little extra effort.   Which is worth it.

That has been my experience, anyway.   But always keep in mind that these are simply guidelines.   Strategies, if you will.   Strategies that have proven useful-enough to other people (like me), that they would recommend those strategies to others.   Your Mileage May Vary,™ but My Mileage™ so far has been pretty darned good.