Here presumably the error is occurring somewhere near unittest. I've tested this and wrote a minimal reproducible example. 

```
import unittest

class TestingError(unittest.TestCase):
    def test_negative_one(self):
        with self.assertRaisesRegex(AssertionError, "xxxxx"):
            self.assertEqual(1, 2)
```

Running this with `unittest discover` or in any other command-line way (like -c) results in frame with -1 while running it from script (with unittest.main probably) does not.

Hope this helps.