No: tests don't change, especially iteratively. If you're editing and re-running your tests in a loop (rather than editing and re-running the code in a loop against the tests), then your tests aren't doing anything related to "testing", because you're changing their pass/fail criteria with each edit. To do so is just to abuse a test suite+test runner as a REPL.

On the other hand, once you know what you're doing, the expectation can be codified into a test (dead code) to assert that the live code maintains an equivalent property with no regressions. A "finished" IPython notebook can indeed be replaced with a regression test to ensure the behavior remains the way you previously determined it to be via experiment. (Though note that this is subtly different from functional testing: you're not asserting any preconceived notion of how an API "should" respond; you're just asserting that the API seems to hold to a certain contract—the one you discovered from your experimentation—and that it's a regression if it then goes against any of the parts of the discovered contract that you had come to rely upon.)