def find(string, substring):
    if len(string) == 0:
        return len(substring) == 0
    elif string[:len(substring)] == substring:
        return True
    else:
        return find(string[1:], substring)
    
def test_find():
    passed = 0
    if find('Ferrer', 'err'):
        passed += 1
    else:
        print("Failed test 1")
    if not find('Ferrer', 'error'):
        passed += 1
    else:
        print("Failed test 2")
    return passed