isolated_notebook_test only works from the repository root

[mpharrigan]

Unlike all other tests, the relative paths in isolated_notebook_test only work if you're running pytest from the repository root. If you're using PyCharm, for example, the test fail when you use the "run pytest on this file" menu action.

Suggest: using something like os.path.dirname(os.path.abspath(__file__)) to find the files in the test. Or: some of the other dev_tools tools query git to find the repo root