import inspect
import unittest


def is_called_by_nose():
    stack = inspect.stack()
    return any(x[0].f_globals['__name__'].startswith('nose.') for x in stack)


class TestFoo(unittest.TestCase):
    def test_foo(self):
        self.assertTrue(is_called_by_nose())

$ python -m nose test_caller
.
----------------------------------------------------------------------
Ran 1 test in 0.009s

OK
$ nosetests test_caller
.
----------------------------------------------------------------------
Ran 1 test in 0.009s

OK
$ python -m unittest test_caller
F
======================================================================
FAIL: test_foo (test_caller.TestFoo)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "test_caller.py", line 14, in test_foo
    self.assertTrue(is_called_by_nose())
AssertionError: False is not true

----------------------------------------------------------------------
Ran 1 test in 0.004s

FAILED (failures=1)