[voiceofunreason]

Well, TDD (or its immediate precursor, depending on where you draw the lines) escaped from the Smalltalk world circa 1997; but I think you can make a case for 1999 being when it really began to emerge. Most of the examples that I saw in the next 5 or so years were written in Java or Python.

Beck's book was 2003, with examples in Java and Python. David Astels wrote a book later that year, again primarily Java but also with short chapters discussing RubyUnit, NUnit, CppUnit.... Growing Object Oriented Software was 2009.

My guess is that "peak" is somewhere between 2009 and 2014 (the DHH rant); after that point there aren't a lot of new voices with new things to say ("clap louder" does not qualify as a new thing to say).

That said, if you're aware of the gap between decision and feedback, and managing that gap, I don't think it matters very much whether that feedback comes in the form of measurements of runtime behavior vs analysis of the source text itself. It might even make sense to use a mixed strategy (preferring the dynamic measurements when the design is unstable, but switching strategies in areas where changes are less frequent).