Yes, I am constantly reducing complexity, but only after first writing tests that cover the reasoning of the program so I know that it won't change. Without some of the "cottage industry" of testing tools, it would take me multiple times longer to write tests, and I would do less reducing of complexity.

And yes, I have seen developers make large changes in their code towards simplicity because it was hard to test.

If someone is going to write complex code, they are going to do it with or without tests. If someone is going to write simple code, tests are a wonderful tool to have in that endeavour.