def interleaveStrings(s1: str, s2: str) -> str:
    """Interleave two strings."""
    s = ""
    for i in range(max(len(s1), len(s2))):
        if i < len(s1):
            s += s1[i]
        if i < len(s2):
            s += s2[i]
    return s


print("Testing interleaveStrings()...", end="")
assert interleaveStrings("pto", "yhn") == "python"
assert interleaveStrings("ab", "xyz?") == "axbyz?"
assert interleaveStrings("a", "b") == "ab"
assert interleaveStrings("xyz", "a b") == "xay zb"
assert interleaveStrings("", "cpcs1") == "cpcs1"
assert interleaveStrings("cpcs1", "") == "cpcs1"
assert interleaveStrings("", "") == ""
print("Passed!")