aider: Created a file 'foo.bad' with non-utf8 characters before calling the 'cmd_add' method.

# Context:
USER: do the todo
ASSISTANT: To complete the TODO, we need to create a file named 'foo.bad' with a non-utf8 encoding. We can use the Python 'codecs' module to create a file with a specific encoding. In this case, we'll use 'iso-8859-15' which is a common encoding that includes characters not present in utf-8.

Here's how to modify the 'test_cmd_add_bad_encoding' method in the 'tests/test_commands.py' file:

```python
tests/test_commands.py
<<<<<<< ORIGINAL
    def test_cmd_add_bad_encoding(self):
        # Initialize the Commands and InputOutput objects
        io = InputOutput(pretty=False, yes=True)
        from aider.coders import Coder

        coder = Coder.create(models.GPT35, None, io, openai_api_key="deadbeef")
        commands = Commands(io, coder)

        # TODO: make a new file foo.bad which will fail to decode as utf-8

        commands.cmd_add("foo.bad")

        self.assertEqual(coder.abs_fnames, set())
=======
    import codecs
    def test_cmd_add_bad_encoding(self):
        # Initialize the Commands and InputOutput objects
        io = InputOutput(pretty=False, yes=True)
        from aider.coders import Coder

        coder = Coder.create(models.GPT35, None, io, openai_api_key="deadbeef")
        commands = Commands(io, coder)

        # Create a new file foo.bad which will fail to decode as utf-8
        with codecs.open('foo.bad', 'w', encoding='iso-8859-15') as f:
            f.write('ÆØÅ')  # Characters not present in utf-8

        commands.cmd_add("foo.bad")

        self.assertEqual(coder.abs_fnames, set())
>>>>>>> UPDATED
```

This will create a file 'foo.bad' with non-utf8 characters before calling the 'cmd_add' method.

tests/test_commands.py

@@ -32,3 +32,20 @@ class TestCommands(TestCase):
         # Check if both files have been created in the temporary directory
         self.assertTrue(os.path.exists("foo.txt"))
         self.assertTrue(os.path.exists("bar.txt"))
+
+    import codecs
+    def test_cmd_add_bad_encoding(self):
+        # Initialize the Commands and InputOutput objects
+        io = InputOutput(pretty=False, yes=True)
+        from aider.coders import Coder
+
+        coder = Coder.create(models.GPT35, None, io, openai_api_key="deadbeef")
+        commands = Commands(io, coder)
+
+        # Create a new file foo.bad which will fail to decode as utf-8
+        with codecs.open('foo.bad', 'w', encoding='iso-8859-15') as f:
+            f.write('ÆØÅ')  # Characters not present in utf-8
+
+        commands.cmd_add("foo.bad")
+
+        self.assertEqual(coder.abs_fnames, set())