Using Unittest/PyTest/etc. to test a Python function that works with files

Question

I have a function that takes in a path to an.mp3 or.m4a file and returns a string containing information extracted from the file using TinyTag (import statement removed for brevity):

def create_search_term(path_to_song):
    tag = TinyTag.get(path_to_song)
    artist = tag.artist
    album = tag.album
    search_term = f"{album} {artist} Album Cover"
    return search_term

I've tested this manually, and it works with a real MP3 file path on my computer. However, I'm trying to add unit tests to this project. Is there a best practice to go writing a unit test for such a function?

A sample use case would be "/path/to/bruce/springsteen/born_to_run.mp3" taken as an input, and "Born to Run Album Cover" as a return value.

Answer 1

Patch out TinyTag to produce a sample response, and then test the function result against that response:

from mock import patch

def test_create_search_term():
    with patch("__main__.TinyTag") as mock_tinytag:
        mock_tinytag.get.return_value.artist = "Bruce Springsteen"
        mock_tinytag.get.return_value.album = "Born to Run"
        assert create_search_term("foo") == "Born to Run Bruce Springsteen Album Cover"