Yup. I often do something like this:

  - write a test for a method that isn't there yet
  - run it, get a red bar, as expected
  - run it in debug mode, and get a debugger
  - write the method implementation in the debugger
  - possibly write other methods that the new method calls, also in the debugger
  - resume the program, get a green bar

Writing code in the debugger is great, because you've got all the runtime state right in front of you, and you can step through the code you're working on. I'd love, love, love to see this in Dart.