Thanks!

I've added more unittests.  They are passing, but I'm getting a callback error that I don't understand.  The same _utest flag that's on the textview dialog didn't seem to work and I was just blindly trying things without success.  Also, the window is briefly opening and closing on the screen.  Any suggestions on where I should look next?

B3 below.  Thanks for the link to that other message.  Combining that with some comments on SO, I tried to find unicode that would be selected by \d and would fail with int(), but couldn't find any.  However, I also realized that the try/except is checking for a TypeError and not a ValueError.  I went and looked at the change history for OutputWindow, but couldn't see anything that would show why there might be a TypeError check here.  If the match group is None, it wouldn't get this far in the code.

Additionally,
1.  I removed 'from tkinter import *' because it wasn't being used.
2.  I changed 'import tkinter.messagebox as tkMessageBox' per issue 30422.
3.  There were two lines:
        edit = self.flist.open(filename)
        edit.gotoline(lineno)
but flist had a gotofileline() that did the same thing.  In the historical code, the 'edit = ' line had and 'or', so maybe that's why it was separated.
4.  *args on the __init__.  I've seen *args used for passing config options and things like that, but I don't understand why it would be preferable here instead of listing the 4 arguments explicitly.

Thanks!