tests/failfilemerge.py

http: use urllib's cookie handler

Split the logic for loading the cookies based on the configuration in a
helper function and otherwise use the library implementation directly.

# extension to emulate interrupting filemerge._filemerge


from mercurial import (
    error,
    extensions,
    filemerge,
)


def failfilemerge(*args, **kwargs):
    raise error.Abort(b"^C")


def extsetup(ui):
    extensions.wrapfunction(filemerge, 'filemerge', failfilemerge)