How would you test this module?

[Gribouillis]

Here is the starting point of a testing file, assuming the initial file is tagfoo.py

# file testtagfoo.py
import unittest as ut
from tagfoo import tagify, tag

class TestTagify(ut.TestCase):
    def test_simple_image_tag(self):
        rv = tagify('image', 'An Image', src='filename.jpg')
        self.assertEqual(
            rv,
            '<image src="filename.jpg">An Image</image>')
        
if __name__ == '__main__':
    ut.main()

You can add methods test_... to the TestTagify class, and create new classes.