Running tests against source code or the package

I've written some Python that I'm distributing as a custom package. I have some tests that I run against the source code while I'm developing, but I also want users who install the package to be able to run the same tests against the distributed package.

My package follows this structure:

my_package
├── my_package
│   ├── __init__.py
│   └── my_module.py
├── setup.py
└── tests
    └── test_my_package.py

The my_package.py is

def my_function():
    print("here!")
    return True

And test_my_package.py is:

import unittest

import sys
sys.path.insert(0, "../")
from my_package.my_module import my_function

class TestMyModule(unittest.TestCase):

    def test_somehting(self):
        self.assertTrue(my_function())

As I'm manipulating sys.path, I'm always running the tests against the development code. Is there a way to use stuptools so I can run the tests against development code but the users run against the installed package?

Thanks!