aider: Import unittest module in tests/test_main.py.

# Context:
USER: I ran this command:

 pytest tests/test_main.py

And got this output:

============================= test session starts ==============================
platform darwin -- Python 3.11.3, pytest-7.3.1, pluggy-1.0.0
rootdir: /Users/gauthier/Projects/aider
collected 4 items

tests/test_main.py F...                                                  [100%]

=================================== FAILURES ===================================
______________________ TestMain.test_main_no_auto_commits ______________________

self = <tests.test_main.TestMain testMethod=test_main_no_auto_commits>

    def test_main_no_auto_commits(self):
>       with unittest.mock.patch("aider.main.Coder") as MockCoder:
E       NameError: name 'unittest' is not defined

tests/test_main.py:37: NameError
=========================== short test summary info ============================
FAILED tests/test_main.py::TestMain::test_main_no_auto_commits - NameError: n...
========================= 1 failed, 3 passed in 1.29s ==========================

ASSISTANT: It looks like the `unittest` module is not imported in the `tests/test_main.py` file. To fix this issue, you need to add the import statement for the `unittest` module at the beginning of the file.

Here's the change:

```python
tests/test_main.py
<<<<<<< ORIGINAL
import os
import tempfile
from unittest import TestCase
from aider.main import main
=======
import os
import tempfile
import unittest
from unittest import TestCase
from aider.main import main
>>>>>>> UPDATED
```

This will import the `unittest` module and resolve the `NameError`.

tests/test_main.py

@@ -1,5 +1,6 @@
 import os
 import tempfile
+import unittest
 from unittest import TestCase
 from aider.main import main
 import subprocess