You met assert in Unit 20. Grouping asserts into test functions, named starting with test_, is the standard way to organise them:

def initials(name):
    return "".join(word[0].upper() for word in name.split())

def test_initials():
    assert initials("ada lovelace") == "AL"
    assert initials("Mary Ann Evans") == "MAE"
    assert initials("prince") == "P"
    assert initials("") == ""

test_initials()
print("All tests passed")

If any assert fails, an AssertionError stops the run, pointing at the failing line, and "All tests passed" never prints. You can add a message to explain a failure: assert initials("x y") == "XY", "two words".