def test_first_empty(): result = add_binary('', '1010') assert (result == None)
def test_example2(): result = add_binary('1010', '1011') assert (result == "10101")
def test_case2(): result = add_binary('111', '101') assert (result == '1100')
def test_both_empty(): result = add_binary('', '') assert (result == None)
def test_example1(): result = add_binary('11', '1') assert (result == "100")
def test_second_nonbinary(): result = add_binary('1010', '1301') assert (result == None)
def test_first_nonbinary(): result = add_binary('1301', '1010') assert (result == None)
def test_second_empty(): result = add_binary('1010', '') assert (result == None)