def test_common_prefix():
"""Test common prefix length of two strings."""
assert utils.common_prefix_length('abcd', 'abce') == 3
def test_differ_length():
"""Test common prefix length of two strings differing in length."""
assert utils.common_prefix_length('abcd', 'ab') == 2
def test_empty_string():
"""Test common prefix length of two strings, one of them empty."""
assert utils.common_prefix_length('abcd', '') == 0
def test_no_common_prefix():
"""Test common prefix length of two strings that have no common prefix."""
assert utils.common_prefix_length('abcd', 'cdef') == 0