Why mock patch leave the original import?

Python Help
1

here is my code

mod.py

from undefined_package import display

def main():
    display()

test_mod.py

from unittest.mock import patch
import unittest
patcher = patch('mod.main')
with patch('mod.main') as MockClass:
  from mod import main
  main()

if __name__ == '__main__':
    unittest.main()

then running test, encountering import error.

thing = __import__(import_path)

File “/home/user/mod.py”, line 1, in
from undefined_package import display
ModuleNotFoundError: No module named ‘undefined_package’

unittest stops when there is a strange package.
I don’t agree with this.

2

Unittest stops when there is any uncaught exception.