added to Ruby

done + added random tests

i had to replace the reference solution though, it seemed to be wrong

• Ruby 3.0 + RSpec + proper describe/it tests' structure
• adds random tests
• !!! the reference solution seemed wrong, which is possible as there were only 3 tests. i replaced it with my own in order to be able to add random tests

PHP should be upgraded to version 8.0

the Elvis operator is not portable though

upgrades to PHP 8.0

fixed + better assertion messages + upgrade to JUnit 5

upgrades to PHP 8.0

moves the testing code out of preloaded section

looks like both are done

• explains the memory model of the output
• makes the initial code compile
• better assertion messages

i resolved the ambiguity by adding the following comment in the C initial code:

// it is guaranteed that s1 and s2 have room for
// 1 + max(strlen(s1), strlen(s2)) bytes

added to the description

• clarifies in the description that the arrays may be of unequal lengths
• adds a comment in the C solution setup about the arrays' sizes in memory

fixed there