> The problem I’ve run into is that when you’re iterating fast, writing code takes double the time when you also have to write the tests.

The times I have believed this myself, often turned out to be wrong when the full cost of development was taken into account. And I came back to the code later wishing I had tests around it. So you end up TDDing only the bug fix and exercising that part of the code with the failing test and then the code correction.