run unittests from a command prompt

I have created python files and unittests but I do not understand how can i run all the tests in one go from command prompt.

file structure

- py
  - __init__.py
  - file1.py
  - file2.py
- tests
  __init__.py
  - test_file1.py
  - test_file2.py

Please let me know the same. when i try to run tests it says me no module name file1, etc