Negative numbers are not prime
Add tests for is_prime
Add used helper functions
Add tests for prime_number_of_divisors
Add tests for sevens_in_a_row
Fix palindrome misspell
Import needed module
Add tests for is_int_palindrome
Add tests for contains_digit
Fix argument alignment
Use plural forms when referring to arguments and add several tests
Do not use names when they are used in only one simple expression
Add tests for contains_digits
Add used helper function
Add tests for is_number_balanced
Add tests for count_substrings
Import needed modules
Add tests for count vowels
Add tests for count_consonants
Add tests for number_to_list